System and process for converting plastic waste to oil products

ABSTRACT

In one aspect, a process is provided for converting thermoplastic waste into hydrocarbon gaseous and liquid products. The process includes: placing in a reactor an amount of thermoplastic to be converted; depressurizing the reactor to remove air; filling the reactor with an inert gas; subjecting the amount of thermoplastic to a thermal plasma arc source operating at a select temperature profile for a preselected residence time to produce a gaseous product; directing the gaseous product through at least one condenser; and collecting a liquid fraction condensed from the gaseous product in the at least one condenser.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication 62/419,819, filed Nov. 9, 2016, the contents of which areincorporated herein by reference in their entirety.

FIELD

The specification relates generally to conversion of plastic waste.

BACKGROUND OF THE DISCLOSURE

Plastic waste is a major environmental problem that exist in millions ofmetric tonnes around the globe. With nearly 288 million tonnes ofplastic production per annum, plastic waste develop large landfillingproblem and has environmental impact (R. Tguado, 2014). Chemicalrecycling includes a chemical reaction called pyrolysis which includescracking of chemical bonds of thermoplastic polymers to hydrocarbongaseous and liquid products. (Vasudeo, 2016) The energy consumptionrequired for the pyrolysis reaction is high due to elevated temperaturesin range of 430-550 C. (G. Grause, 2011) and 30-45 minutes reactionresidence time. The amount of energy estimated for pyrolysis reaction isaround 1047 KJ/kg which can be achieved by thermal plasma with moreenergy efficiency at a lower cost. Thermal plasma consumes electricenergy to product high efficiency heat and shows much highertemperatures than required by pyrolysis, gasification or otherindustrial heat consuming applications. Also, thermal plasma is moreenvironmental field since it relies on conversion of electrical energyto heat rather than burning natural gas or fuels for a heat source.Since reactors can operate in a time range of 20-25 years, thermalplasma is a more sustainable, cost effective and environmental friendlyreplacement in comparison with traditional heating methods such asindustrial furnaces.

SUMMARY OF THE DISCLOSURE

In one aspect, a process is provided for converting thermoplastic wasteinto hydrocarbon gaseous and liquid products. The process includes:

placing in a reactor an amount of thermoplastic to be converted;

depressurizing the reactor to remove air;

filling the reactor with an inert gas;

subjecting the amount of thermoplastic to a thermal plasma arc sourceoperating at a select temperature profile for a preselected residencetime to produce a gaseous product;

directing the gaseous product through at least one condenser; and

collecting a liquid fraction condensed from the gaseous product in theat least one condenser.

In another aspect, a process is provided for converting thermoplasticwaste into hydrocarbon gaseous and liquid products. The processincludes:

receiving a feedstock of thermoplastic to be converted;

granulating the feedstock to reduce the thermoplastic to a preselectedgranule size;

delivering the granulated feedstock to a preheat unit and preheating thegranulated feedstock based on a preselected preheat temperature profile;

delivering the preheated granulated feedstock into a reactor andsubjecting the feedstock to pyrolysis based on a preselected pyrolysistemperature profile for a preselected residence time to produce agaseous product;

directing the gaseous product through at least one condenser; and

collecting a liquid fraction condensed from the gaseous product in theat least one condenser.

BRIEF DESCRIPTIONS OF THE DRAWINGS

For a better understanding of the embodiments described herein and toshow more clearly how they may be carried into effect, reference willnow be made, by way of example only, to the accompanying drawings inwhich:

FIG. 2-1 is a schematic diagram illustrating the thermoplastic polymerto pyrolysis oil expected end-products (A. Onwudili, 2009);

FIG. 2-2A is a simplified sectional view of a plasma fixed bed reactor(L. Tang, 2013);

FIG. 2-2B is a simplified sectional view of a moving bed reactor design(L. Tang, 2013);

FIG. 2-3 is a bar graph illustrating the annual plastic waste deposition(Jambeck, 2015);

FIG. 2-4 is a diagram illustrating branched and unbranched polymers(university, 2016);

FIG. 2-5 is a graph showing the three stages of PETE by thermal analysis(Wunderlich B., 2005);

FIG. 2-6A and FIG. 2-6B are simplified schematic illustrations ofnon-transferable and transferable arc generators (L. Tang, 2013);

FIG. 2-7 is a schematic diagram of a RF plasma system with inductivecoil. (L. Tang, 2013);

FIG. 2-8 is a schematic diagram of a microwave plasma torch (L. Tang,2013);

FIG. 3-1 is a flow chart illustrating a research methodology for thermalplasma circuit design;

FIG. 4-1 is a graph illustrating thermal cracking at 350° C. and 400° C.of a thermoplastic waste mixture (Kyong-Hwan Lee, 2007);

FIG. 4-2 is a bar graph showing product yields in wt % of individualplastics and obtained at 5 C/min, maximum temperature 500° C. (Paul T.Williams, 2006);

FIG. 4-3 is a graph showing the relationship between the decompositiontemperature and the dissociation energy (José Aguado, 1999);

FIG. 4-4 shows the general mechanism for the thermal degradation ofaddition polymers (José Aguado, 1999);

FIG. 4-5 is a graph showing a thermogravimetric analysis of HDPE andLDPE in a nitrogen atmosphere (D. P, 1999);

FIG. 4-6 is a graph of a GC analysis of the oils obtained by LDPEcracking at 420° C., 90 min (José Aguado, 1999);

FIG. 4-7 is a graph showing a thermogravimetric analysis of PP in anitrogen atmosphere (D. P, 1999);

FIG. 4-8 is a graph showing a TG analysis of PS in a nitrogen atmosphere(José Aguado, 1999);

FIG. 4-9 is a graph showing the degree of dehydrochlorination of PVC at150° C. as a function of time (José Aguado, 1999);

FIG. 5-1 shows non transferred direct current thermal plasma mechanicaland electrical components;

FIG. 5-2 is a perspective image of a direct current thermal plasma jet;

FIG. 5-3 is a perspective image of a direct current thermal plasma jetin a vacuum chamber;

FIG. 5-4 is a side view of a direct plasma generation over a ceramicnozzle;

FIG. 5-5 is a side view of a direct thermal plasma temperature 890° C.using K-type thermocouple;

FIG. 5-6 is a circuit diagram of the direct current thermal plasmacircuit;

FIG. 5-7A is a circuit diagram of the half wave rectifier using a diodefor AC power supply;

FIG. 5-7B is a graph showing output from the half-wave rectifier;

FIG. 6-1 is a schematic diagram of a pyrolysis experimental setup;

FIG. 6-2 is a perspective view of a vacuum chamber with non-transferredDC thermal plasma circuit and metal electrodes;

FIG. 6-3 is a side view showing DC thermal plasma emissions on a 15 gLDPE sample;

FIG. 6-4 is a perspective view showing the thermal plasma emissionthrough a direct current ceramic nozzle setup;

FIG. 6-5 is a plan view showing a molten 15 g LDPE sample at 230° C. ofthermal plasma heating;

FIG. 6-6 is a perspective view showing that the LDPE plasma samplestarts to reduce in size and melt under direct current thermal plasma;

FIG. 6-7 is a perspective view showing a thermoplastic conversion usinga laboratory electric heater;

FIG. 6-8 is a perspective view showing releasing gaseous productsthrough a condensation system;

FIG. 7-1 is a graph showing temperature profiles in degrees Celsius ofthermal plasma and thermal cracking heater;

FIG. 7-2 is a view of a condensed oil sample on the reactor lid from a15 g LDPE thermoplastic in a pyrolysis reaction at 540° C. and 30minutes;

FIG. 7-3 is a perspective view of an oil sample collected from 15 g LDPEunder 540° C. and 30 minutes in pyrolysis (nitrogen) conditions;

FIG. 7-4 is a graph showing the gas chromatography results of an oilsample collected from 15 g of LDPE using headspace GC with FID;

FIG. 7-5 is a graph showing the GC analysis with FID identifying C 10, C16 and C 34 for an oil sample;

FIG. 7-6 is a perspective view of showing the ignition test ofhydrocarbon gases from pyrolysis reaction;

FIG. 7-7 is a plan view of a 15 g LDPE sample (reactant) for a pyrolysisreaction;

FIG. 7-8 is a plan view of a tar sample collected from 15 grams of LDPEin a pyrolysis reaction;

FIG. 7-9 is a perspective view of the 7 mL pyrolysis oil calculated from15 g of LDPE in a pyrolysis reaction;

FIG. 8-1 block flow diagram of the structure of a chemical engineeringproject (Roberth, Perry, 2008);

FIG. 8-2 is process flow diagram for processing plastic waste;

FIG. 8-3 is a process flow diagram of a 10 metric tonne per hourthermoplastic pyrolysis plant;

FIG. 8-4 is a bar graph showing the energy consumption in major processunits in a thermoplastic-to-oil facility;

FIG. 8-5 shows a computer display with an S1 inlet stream specification;

FIG. 8-6 shows a computer display with the material properties-includingpolymers in the process system material stream;

FIG. 8-7 shows a computer display with the thermoplastic componentsadded to chemical properties in Aspen HYSYS®;

FIG. 8-8 shows a computer display with a selection of Stream Classes forPSD simulation;

FIG. 8-9 shows a computer display with input components of reactants andproducts;

FIG. 8-10 shows a computer display with the expected petroleum productsfrom pyrolysis reactions;

FIG. 8-11 shows a computer display with pyrolysis reactorspecifications;

FIG. 8-12 shows a computer display with stop criteria and operationtimes for a pyrolysis reactor;

FIG. 8-13 is a schematic diagram showing a plastic granulator energysimulation;

FIG. 8-14 shows a computer display with the specifications of a plasticsolid granulator;

FIG. 8-15 is a schematic diagram showing a thermoplastic preheater from30 to 250° C.; and

FIG. 8-16 shows two block diagrams of two selected process systems forLCA.

DETAILED DESCRIPTION

In the present disclosure, following is a list of abbreviations andacronyms used:

A Plasma Area

AC Alternating Current

BFB Bubbling Fluidized Bed

C Reaction Conversion

CFB Circulating Fluidized Bed

DC Direct Current

EPS Expanded Polystyrene

FID Flame Ionization Detector

FTIR Fourier Transform Infrared Spectroscopy

GC Gas Chromatography

H SI unit of inductance

HC Hydrocarbon Element

HDPE High Density Polyethylene

KTA Kilo tonne per annum

LCA Life Cycle Assessment

LDPE Low Density Polyethylene

LPG Liquefied Petroleum Gas

m Total Plasma gas mass flow

MPW Municipal Plastic Waste

n Reaction Order

PE Polyethylene

PBD Process Block Diagram

PFD Process Flow Diagram

PP Polypropylene

PS Polystyrene

PSD Particle Size Diameter

PVC Poly Vinyl Chloride

r Radial Position

R Channel Radius

RF Radio Frequency

TGA Thermogravimetric Analysis

W Weight

wt Weight Percentage

In the present disclosure, following is a list of identifiers ofproperties used:

Ao Reaction Rate Exponential Factor

Ea Reaction Activation Energy

h Enthalpy of Plasma Jet

h_(ave) Specific Enthalpy Flow

Mn Number Average Molecular weight

Mw Mass Average Molecular weight

ni Ion Atom Density

nn Neutral Atom Density

p Density Of Plasma Jet

pF Pico Farad (10-12 Farad)

T50 Temperature at which 50% mass loss of initial reactant occurs

T_(ave) AveragePlasmaTemperature

Tc Crystallization Temperature

Tg Polymer Glass Temperature

Tm Melting Temperature

TP Composition Temperature

Ui Ionization Energy

Wo Mass of Product Oil

Wi Initial Mass Sample

W∞ Final residual mass

t residence time

For simplicity and clarity of illustration, where consideredappropriate, reference numerals may be repeated among the Figures toindicate corresponding or analogous elements. In addition, numerousspecific details are set forth in order to provide a thoroughunderstanding of the embodiments described herein. However, it will beunderstood by those of ordinary skill in the art that the embodimentsdescribed herein may be practiced without these specific details. Inother instances, well-known methods, procedures and components have notbeen described in detail so as not to obscure the embodiments describedherein. Also, the description is not to be considered as limiting thescope of the embodiments described herein.

Various terms used throughout the present description may be read andunderstood as follows, unless the context indicates otherwise: “or” asused throughout is inclusive, as though written “and/or”; singulararticles and pronouns as used throughout include their plural forms, andvice versa; similarly, gendered pronouns include their counterpartpronouns so that pronouns should not be understood as limiting anythingdescribed herein to use, implementation, performance, etc. by a singlegender; “exemplary” should be understood as “illustrative” or“exemplifying” and not necessarily as “preferred” over otherembodiments. Further definitions for terms may be set out herein; thesemay apply to prior and subsequent instances of those terms, as will beunderstood from a reading of the present description.

Any module, unit, component, server, computer, terminal, engine ordevice exemplified herein that executes instructions may include orotherwise have access to computer readable media such as storage media,computer storage media, or data storage devices (removable and/ornon-removable) such as, for example, magnetic disks, optical disks, ortape. Computer storage media may include volatile and non-volatile,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer readableinstructions, data structures, program modules, or other data. Examplesof computer storage media include RAM, ROM, EEPROM, flash memory orother memory technology, CD-ROM, digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed by anapplication, module, or both. Any such computer storage media may bepart of the device or accessible or connectable thereto. Further, unlessthe context clearly indicates otherwise, any processor or controller setout herein may be implemented as a singular processor or as a pluralityof processors. The plurality of processors may be arrayed ordistributed, and any processing function referred to herein may becarried out by one or by a plurality of processors, even though a singleprocessor may be exemplified. Any method, application or module hereindescribed may be implemented using computer readable/executableinstructions that may be stored or otherwise held by such computerreadable media and executed by the one or more processors.

1. Problem Definition

The heat energy needed for the pyrolysis reaction of thermoplastics inabsence of oxygen limits its implementation on industrial scale due tohigh operating cost and very high temperature profiles. Thermal plasmatechnology high performance and efficiency used in pyrolysis reactioncan reduce energy consumption and provide a cleaner energy alternativethat delivers high thermal energy using the Plasma circuit that can beused in pyrolysis reaction. The thermal plasma circuit is built and usedin the experimental setup and tested in nitrogen conditions closedsystem conditions.

The project utilizes a direct current thermal plasma torch at elevatedtemperatures above 550 C to heat thermoplastic mixtures of LDPE, HDPE,PS, PP or PETE in an oxygen starved environment using pure nitrogen99.99% in a pyrolysis reaction releasing hydrocarbon products in form ofgas or liquid, waxes and tar. Analytical results aim to calculate theproduct yield and energy efficiency using electric heaters againstthermal plasma torch. The solution approach is to develop a closedsystem vessel with a thermoplastic mixture and nitrogen gas environment(absence of oxygen) allowing calculating the performance of the reactionand product yields with electric heaters against the plasma torches in alaboratory scale. Also, the electric circuit of the thermal plasma torchincluding the limitations and performance criteria in the plasma circuitas well as the temperature profile. The electrical consumption of thethermal plasma system is 270 W converting alternative current powersupply to a 9000V, 30 mA 270 W power.

An objective is to provide an alternative system that utilizes thermalplasma torch in the pyrolysis reaction converting thermoplastics to oilproducts replacing the use of other thermal equipment with thermalplasma torch. The thermal plasma should reduce energy consumptions, moreenergy efficiency that other heating methods. In our project there aretwo experimental setups. Experiment 1 will include 1056 W electricheater that will heat the closed system including the thermoplasticmixture. Experiment 2 will include direct current thermal plasma torchwhich will be used instead of other heating methods. A temperatureprofile for both experiments as well as product yields and energyefficiency will be calculated. The final objective is to assess theperformance of a direct current thermal plasma arc setup to be used inthe thermoplastic pyrolysis conversion reaction and calculate theproduct yield of pyrolysis oil as well as gas chromatography results toinvestigate the existing chemical composition of hydrocarbon liquids.

The research scope is to design and evaluate the performance of a Directcurrent thermal plasma torch that can convert thermoplastic waste to oilproducts with a reaction residence time of 30 minutes in a closed systemreactor vessel (1 Litre) on a 15 g thermoplastic sample to be convertedto oil products ranging from hydrocarbon gas, liquid, waxes and tar. Theexperiments are carried in pure nitrogen conditions to avoid oxidationreactions. A 220V, 4.8 A electric heater is used to compare performancewith DC thermal plasma setup and oil samples are analyzed by GCchromatography to identify the chemical composition of pyrolysis oil.The energy consumptions are calculated for major process units for apyrolysis chemical plant.

Plastics are inexpensive, easy to mold and lightweight. Plasticproperties has many advantages which makes them very promising forcommercial applications. However, the problem of recycling still is amajor challenge. There are both technological and economic issues thatrestrain the progress in this field. A slower development within thefield of recycling creates a serious problem were 100 of millions ofmetric tonnes of used polymeric materials are discarded every yeararound the globe (Nations, 2009). It leads to ecological andconsequently social problems. Waste deposition in landfills becomesincreasingly unattractive because of its low sustainability, increasingcost, and decreasing available space. Most common types ofthermoplastics such as polyolefins (HDPE, LDPE, LLDPE, PP) andpoly-aromatics (PS, EPS) can be easily separated from MSW usingcommercially available density-based separation methods (G. Dodbiba,2002). While recycling of plastics will solve this problem, it will alsobe economically beneficial as the market price of waste plastics asstarting materials is at present particularly low. The differentpathways for plastic recycling (Igor A. Ignatyev, June 2014) explainedin waste plastic recycling techniques section.

This project aims to design and implement a process system forthermoplastic waste conversion through pyrolysis to selected oilproducts utilizing heated plasma arc Technology as a heating sourceinstead of traditional heating mechanisms at a more economical energycost instead of using traditional fossil fuel heaters (e.g. gasfurnaces) in the thermal cracking process of thermoplastic waste to oilproducts at the pyrolysis reactor stage. Aspen HYSYS V8.8 simulationswill be used and supported by experimental setup and laboratory results.

The research thesis focuses on five main types of thermoplastics whichare LDPE, HDPE, PS, PP and PETE with plastic compositions that matchrealistic statistics of MPW in Ontario and Canada. The system rejectsnon-plastic components as well as thermosetting plastics. The mainprocess stages for large scale chemical plants are granulation,preheating, pyrolysis reactor, condensation (heat recovery) and storage.

Also, the pyrolysis reactor is evaluated by using Fired gas furnace insimulation and electric heaters in experimental results in comparisonwith heated plasma at the University of Ontario Institute of Technology(UOIT)—Energy Safety and Control Lab. A novel pyrolysis reactor andexperimental setup analyzes pyrolysis reaction performance and energyconsumption with and without Direct (DC). The laboratory equipment usedin our experiment is nitrogen pressurized gas cylinder (4.5 Nm3), 1056 Welectric heater, closed system reactors, Pyrex glass condensationsystem, mass scale, which will be elaborated further in this disclosure.

The experimental setup carries the thermoplastic pyrolysis reactionusing electric heater in experiment 1 and heated plasma source inexperiment 2. The results in terms of energy consumption, efficiency andfinal products are analyzed. A K-type thermocouple is used to create atemperature profile in all the experimental setups.

The thermal plasma electric circuit is explained in this report andtemperature profile is developed to compare the thermal plasmaperformance in the pyrolysis reactions.

2. Description of Recycling Methods and Technologies 2.1. Waste PlasticsRecycling Methods

There are two main types of plastic polymers: Thermoplastics andThermosetting polymers.

Thermoplastics can repeatedly soften and melt if enough heat is appliedand hardened on cooling and their melting points range from 120-240C-Biron. 2007/. Examples are polyethylene, polystyrene, polyethylenetetraphalate, polystyrene and polyvinyl chloride, among others. In thisproject we will mainly focus on five types of thermoplastics includingLDPE, HDPE, PS, PP, and PETE. However, the pyrolysis process can acceptany type of thermoplastics as feedstock. (Igor A. Ignatyev, June 2014)

Thermosetting can melt and take shape only once. They are not suitablefor repeated heat treatments. Therefore, after they have solidified,they stay solid. Examples are phenol formaldehyde and urea formaldehyde.(Y B Sonawane, 2009) Thermosetting plastics are considered as rejectedmaterials in our chemical process system due to decomposition andinability to convert to any useful products. Below are possible routesof plastic recycling.

2.1.1. Mechanical Recycling

Primary mechanical recycling is the direct reuse of uncontaminateddiscarded before reintegration of a used material into a new product,the process involves shredding, crushing or milling. This step is vitalas it makes the material more homogeneous and easier to blend withadditives and other polymers for further processing. It is also known asclosed loop recycling. The best-known methods of this type of processingof mechanical recycling are injection molding, extrusion, rotationalmolding, and heat pressing. Therefore, only thermoplastic polymers, suchas LDPE, HDPE, PP, PE, PETE, and PVC, can normally be mechanicallyrecycled. (Igor A. Ignatyev, June 2014)

This method is applicable for uniform and uncontaminated thermoplasticwaste while the main problems associated with primary recycling aredegradation of the material resulting in a loss of properties asappearance, mechanical strength, chemical resistance, andprocessability. (Roy, 2006) Contamination highly affects the primarymechanical recycling process and causes quality degradation.

2.1.2. Secondary Mechanical Recycling

This type of recycling involves modification of the material/productwithout the use of chemical processes. Purity grade of polymers maybenot known therefore could be recycled in secondary mechanical recyclingloop which involves separation and purification. The polymer is notchanged during the secondary recycling but its molecular weight fallsdue to chain scissions, which occur in the presence of water and traceamounts of acids. This may result in the reduction of mechanicalproperties. Another reason for the drop in mechanical properties afterrecycling is the contamination of the main polymer (matrix) with otherpolymers. (i.e., their blends have mechanical properties that areinferior to those of the pure constituents. (Igor A. Ignatyev, June2014). Another approach to secondary recycling reprocessing is melthomogenization using specialized equipment, use of ground plastics wasteas a filler, and separation into single homogeneous fractions forfurther processing, such as partial substitution of virgin resins andblending with other thermoplastics using suitable equipment. (Roy, 2006)

An example are PETE impurities in PVC, in which solid PETE lumps form inthe PVC-phase. This leads to significantly downgraded properties andconsequently less-valuable end products.

2.1.3. Chemical Or Tertiary Recycling

Chemical Recycling is a type of polymer recycling in which a polymerchains are converted to smaller molecules through chemical process.Examples of such processes are hydrolysis, pyrolysis, hydrocracking andGasification. Typical conversion feedstock are in liquid/molten stateused for production of fuels, new polymers, and other chemicals. (Biron,2007). Feedstock recycling is a type of polymer recycling in whichpolymer chains are converted to smaller molecules through chemicalprocesses. Examples of such processes are hydrolysis, pyrolysis,hydrocracking, and gasification. Typical conversion products are liquidsand gases, which can be used as feedstock for the production of fuels,new polymers, and other Chemicals. A major part of a polymer crackingprocess is pyrolysis in a fluidized bed reactor. It leads to formationof a fluid fraction (wax). This fraction is then transferred tothermocatalytic and catalytic crackers of a refinery for furtherreprocessing. (Igor A. Ignatyev, June 2014)

Preparation for cracking includes grinding, removal of metals, and othercoarse components in large scale production plants and not necessary insmall scale or laboratory setups. Then, the plastic waste is fed into afluidized bed pyrolysis reactor at a temperature of 500 C for cracking.Dust is removed from the gas phase by a cyclone. Subsequently, HCl,which is generated by pyrolysis of chlorine-containing polymers such asPVC, is quenched over a CaO (Calcium Oxide) bed. (Igor A. Ignatyev, June2014). It is recommended to treat PVC by removal of Chlorine ions beforeallowing the molten PVC liquid to enter the Pyrolysis Reactor. Thiscould occur in a gas-liquid fluidized bed reactor (A. López, 2011) at280-320 C, where Chlorine ions is converted to HCl and separated fromthe molten polymer. This step is carried out before treatment of PVC ina Pyrolysis reactor. (G. Yuan, 2014) Thus, it is recommended to avoidsimulation and experimentations on PVC (polyvinyl chloride) since ituses further treatment of chlorine removal at 280-320 C to avoidcontamination in the pyrolysis reactor.

In a pyrolysis reactor gas and liquid phase are produced. The latter iscooled to isolate its condensable part using condensers and coolers. Thecondensate (wax) is further processed in a refinery. The non-condensablefraction (C₁-C₄) is pressurized, heated, and stored in Pressurizedgaseous vessels or transported as petroleum gas. The excess is used forheat generation and implemented to optimize the process design. Certainenvironmental impacts (e.g., emission of dioxins) and intensive energyconsumption explain why feedstock recycling is mostly limited tosmall-scale pilot projects. Through our plasma arc technology pyrolysisreactor, energy consumption is evaluated and compared with usingelectric heaters. Expected products are Gasoline, diesel, andkerosene-range chemicals are expected to be produced at a maximum oilyield of 87.5%. (Igor A. Ignatyev, June 2014). Char is also expected tobe an undesired by-product as seen in the schematic image in FIG. 2-1.

Different reaction kinetic models have been developed in academicpublications to model the simultaneous pyrolysis reactions which is achallenging task to achieve. Reactors can be modelled usingstoichiometric model, Yield model, equilibrium model, continuous stirred(CSTR) model, Plug flow model, or Batch reactor. (Don W. Green, 2008).In our simulation, yield reactors are used and pyrolysis energy reactorenergy consumption required per kg is required experimental results.

2.2 Thermal Plasma Reactor

As a proposed solution, a Plasma Arc Pyrolysis reactor is proposed andevaluated that converts thermoplastic waste to oil products (LDPE, HDPE,PP, PS and PETE) at 450-550 C and atmospheric pressure in inertconditions (N₂ gas environment). Below are proposed solutions fordifferent designs of a plasma arcs used in gasification reactors.According to the following reactors setup technologies were carried outfor a pyrolysis reactions of waste plastics. (L Tang, 2013)

Cyclonic Reactor

Circulating fluidized bed (CFB)

Bubbling fluidized bed (BFB)

Twin screw reactor

Stirred Reactor

Ablative reactor

Vacuum and plasma reactors.

Spouted bed

Rotating cone

Possible illustrated thermal plasma designs in reactors are describedbelow:

2.2.1 Thermal Plasma Torch Fixed/Moving Bed Reactor

A plasma fixed/moving bed reactor, as shown in FIGS. 2-2A and 2-2B aresimple types of plasma reactor, namely a plasma moving bed reactor (FIG.2-2A) and a plasma fixed bed reactor (FIG. 2-2B), which have a bed ofplastic waste particles with a feeding unit, shredder or granulator, anash removal unit and a gas exit. For a plasma fixed bed reactor, thewaste is put in the center of the reactor while for plasma moving bedreactor, the waste enters the reactor through a point at the top or theside of the reactor and, after contact with the ionized gas, the metalsand ash form a liquid pool at the bottom of the reactor. After, thethermoplastic waste is pyrolyzed, and the gaseous products rises, andexits at the top of the reactor to condensation systems. Condensedliquids are analyzed using analytical equipment such as gaschromatography or FTIR (Fourier transform infra-red spectroscopy). Thefollowing GC chromatography methods are used:

-   -   Headspace analysis to a gas chromatography with a FID (Flame        ionization detection)—determination of C6-C10 Analysis    -   Gas chromatography with solvent and separated using FID (Flame        ionization detection).

There are two approaches to the current design of the plasma fixed andmoving bed plasma reactors, whether the plasma jet is located outside orimmersed inside. In the first approach, promoted by Westinghouse andHitachi, a non-transferred torch is located outside of the reactor. Thehot gas then flows from the torch into the waste reactor to melt andgasify the thermoplastic mixture as we can see in FIGS. 2-2A and 2-2B.The second approach is an in-situ torch, the plasma torch is immersedinside the reactor itself. This torch can either be a non-transferredtorch or a transfer torch (L Tang, 2013). Plasma fixed bed and movingreactors are simple to construct and have been commonly used in pilotplant with continuous waste feed mode or batch mode. Their advantagesinclude better heat transfer to feedstock and waste continual contactingwith plasma, resulting in more complete waste conversion.

2.2.2 Pyrolysis Reactor Design and Operation

As mentioned above, plasma temperatures can reach very high, e.g. up to1200 C, delivering high reaction temperatures which was used previouslyin incineration. Our project job scope is to convert thermoplastic wasteproducts separated from municipal plastic waste to oil products byutilizing arc plasma energy the pyrolysis reaction. There is a largefraction of electrons, ions and excited molecules together with the highenergy radiation. When carbonaceous particles are injected into aplasma, they are heated very rapidly by the plasma releasing volatilematter giving rise to hydrogen, and light hydrocarbons such as methane,ethane and heavier components such as cyclohexane depending on theoperating conditions of the reactor. (L Tang, 2013) The pyrolysisreactor has the following design and operating conditions:

Main Process Design Features

Feed Thermoplastic Waste (LDPE, HDPE, PP, PS, PETE) Mass Fraction usedin LDPE: 0.20|HDPE: 0.20|PETE: 0.40 Large scale Simulation PS: 0.10|PP:0.10 Process Pyrolysis (N2) Main Equipment Batch Reactor (BR) SpecialFeatures DC Arc Plasma Gasifier Main Product Hydrocarbon Oil, Gas, WaxOperating Pressure −0.95 bar Operating Temperature 480-540 C. ReactorClassification BR (Batch Reactor) (Roberth. Perry, 2008) ReactorAtmosphere N2 gas 99.999% Catalyst No Catalyst added Reaction residencetime 30 minutes

2.2.2.1 Expected End-Products

Undesired Reactions in a thermal plasma pyrolysis is partial thermaloxidation reaction, which results in a high proportion of gaseousproducts (carbon dioxide, water, carbon monoxide, hydrogen and gaseoushydrocarbons), small quantities of char (solid product), and ash. Thisis prevented by using an inert gas such as nitrogen in a closedpyrolysis reactor. Nitrogen gas prevents oxidation and undesiredreactions. This type of partial oxidation reaction is undesired andshould be avoided or minimized to maximize the yield of usefulhydrocarbons. (L Tang, 2013)

2.3 Global and Municipal Plastic Waste Statistics

Municipal plastic waste is collected by municipalities that covers wastefrom households, including bulky waste, commerce and trade waste, officebuildings, used electronics, institutions as well as construction anddemolition waste. In Ontario, The Environmental Protection Act (EPA)(1990) regulates the residential waste management and recycling serviceswhich are mandated under the Recycling and composting of municipal Wasteregulation. (Giroux, 2014) The global plastic waste production isestimated around 250 million tonnes which show the huge potential ofthermoplastic waste to oil conversion (Jambeck, 2015) on in a pyrolysisreaction. FIG. 2-3 shows a graph of plastics waste statistics generatedglobally.

The graph in FIG. 2-3 shows the huge potential for chemical recycling ofthermoplastic waste to pure oil products with a global production ofmore than 270 million metric tonnes of deposited plastic waste. Plasticwastes have also showed an exponential growth over the last 60 yearswith an increase of nearly 20 times from 5 million tons in 1950 tonearly 100 million tons. (M. Syamsiro, 2014)

2.4 Chemical and Physical Properties of Plastic Mixture

As our feed system will involve a mixture of thermoplastic waste, it isvital to investigate thermoplastic waste melting properties in order toutilize such information in the conceptual design stage. Plastics unlikeother elements could decompose before its melting point, thereforethermoplastics properties are to be studied and experimented throughoutthe project. Important thermoplastics that will be converted to oilproducts are LDPE, HDPE, PS, PP, and PETE. Below are some physicalproperties of virgin thermoplastics gathered from (Biron, 2007)

Plastic Type Physical LINEAR Homopolymer Property LDPE HDPE PE PP PSPETE Density 0.917-0.940 0.940-0.970 0.915-0.950 0.90-0.91 1.05 1.3-1.4(g/cm³) Softening  76-109  80-120  90-110 154 84-106 70 Point (C) Glass−110 −110 −110 −10 90 67 Transition Temperature (Tg) Melting 110-120 130122-124 168-173 240 220 Temperature Tm (C.) Thermal 0.32-0.35 0.40-0.500.35-0.45 0.15-0.21 0.16 0.21 conductivity (W/m · K) Specific heat 0.550.55 0.55 0.46 0.32 0.31 (cal/g C) 2.3012 2.3012 2.3012 1.92464 1.33881.29704 KJ/Kg C

These properties are used in calculating the heat duty required to raisea thermoplastic mixture to pyrolysis temperatures in absence of oxygen.All operations in a pyrolysis plant need to be below glass temperaturesto avoid the plastic glass state which is brittle and can destroyrotating equipment such as pumps.

The oil products expected to be produced are categorized and illustratedas below:

Heavy Fuel Fuels LPG Gasoline Kerosene Diesel Oil Hydro- C3 to C4 C4 toC12 C12 to C12 to C24 C12 to C70 carbons C15

The molecular structure of LDPE and HDPE which shows branched andunbranched polymers is shown in FIG. 2-4.

In pyrolysis reactions, in pyrolysis process, cross linked polymer willcrack rather than melt or evaporate. The heat supplied in a pyrolysisreaction will break the intermolecular bonds in the polymer structureinto shorter petroleum range compounds such as LPG, gasoline, diesel andheavy oil.

Three stages of a heated polymer are represented in FIG. 2-5 and includeglass transition, melting and decomposition as temperature increases. Asmentioned in FIG. 2-5, as the temperature increases, the thermoplasticstart with glass transition phase followed by cold crystallization andmelting. For PETE as shown in FIG. 2-5 after 530 K the plastic changesto a molten plastic, and start decomposing at Tp around 680 K (406.85C).

2.5 Thermal Cracking Properties of Thermoplastic Waste Mixtures

It was mentioned above that our thermoplastic mixture is composed mainlyof HDPE, LDPE, PP, PETE, PVC and PS. These polymer structures accountfor above 70% in waste plastics globally (D. P, 1999). It is also to benoted that in pyrolysis mixed plastics are more complex that pureplastics and thus plastic waste mixture in pyrolysis reactions behavedifferently than pure plastics under the same conditions due to changesin chemical and physical properties of different plastic wasteinteraction in a mixture. (Vasile, 2001). Thus the quality of oilproducts is affected depending on the plastic waste mixture composition.The plastic type had an influence on the yield, molecular weightdistribution and product distribution as a function of the reactionresidence time. (Kyong-Hwan Lee, 2007). One of the primary tools ofthermal cracking experimental equipment is the TGA for reactants at acontinuous heating rate (for e.g. 5 C/min, 10 C/min) in order to measuremass loss per minute from which reaction conversion can be determined.

2.5.1 Experimental Techniques in Pyrolysis Reactions

The following analytical equipment are used to analyze the performanceand temperature and mass profile of the thermoplastic mixture inpyrolysis reaction.

2.5.1.1 TGA (Thermogravimetric Analysis)

TGA (Thermogravimetric analysis) is an experimental analysis techniquein which changes in physical and chemical properties of materials aremeasured as a function of increasing temperature under a constantheating rate. Through TGA, the physical and chemical properties of thepyrolysis chemical reaction can be investigated. TGA can provide usefulparameters for our pyrolysis reaction including second-order phasetransitions, vaporization, and the chemical phenomena, decomposition andsolid-gas reactions.

2.5.1.2 TGA T50 Results of Different Plastic Mixtures

TGA T50 results of different plastic mixtures refers to the degradationtemperature at which weight loss of reactants amounts to 50%, or inother words the temperature at which 50% of a reactant is changed to aproduct. The following T50 TGA is expected from the followingthermoplastic types: (Kyong-Hwan Lee, 2007)

Polystyrene T50: 440 C

Polypropylene T50: 455 C

Polyethylene T50: 480 C

Thus the order of degradation temperature of waste thermoplastic mixturewas PS<PP<HDPE<LDPE Among pure reactants, PS with polycyclic structuredegrades at lowest temperature, while PP in polyolefinic polymers wasdegraded at lower temperature than PE. From the results it can beexpected that plastic mixture of different compositions will result indifferent production characteristics. (Kyong-Hwan Lee, 2007)

2.5.2 GC-MS (Gas Chromatography-Mass Chromatography) Spectroscopy

The liquid and gas samples from pyrolysis reactions are analyzed viaGC-MS ((Gas Chromatography-Mass Chromatography) Spectroscopy) todetermine hydrocarbon chain distribution in terms of paraffins, olefins,and aromatics. (J. Zeaiter, 2014). The gas chromatographer alsodetermine the physical structure of the liquid or gas sample dependingon retention times utilizing computer matching databases.(Urionabarrenchea, 2012).

2.6 Plasma Engineering

Advancement in thermal plasma torches have resulted that this technologyis becoming a viable solution for chemical processes. The mainadvantages of plasma are its ability to control process chemistry and tobuild small footprint reactors due to its high energy density andreactivity of the free radicals that are produced. (L. Rao, 2013). Bothtransferred and non-transferred plasma torches can be used as a sourceof heat. Industrial plasmas can be classified as thermal plasmas andnon-thermal plasmas.

Thermal plasma is typically established between any two currentconducting electrodes separated by an insulator. A plasma forming gas isblown between the two conducting electrodes resulting in a hightemperature plasma plume. A plasma torch generates and maintains anelectrically conducting gas column between the two electrodes: a cathode(negative electrode) and an anode (positive electrode) (D. Harbec,2004).

This plasma setup is termed as non-transferred (NT) plasma torches. TheDC Power Plasma works with any oxygen free inert gas, such as argon,nitrogen, helium and/or a mixture of the above gases, as the plasmaforming gas. (L. Rao, 2013) This plasma setup is very suitable since ourgas medium needed in the pyrolysis reaction is high purity nitrogen.

The main advantages of thermal plasma offer to treatment processes arethe following:

-   -   Rapid heating and reactor start-up. (This is also supported by        our temperature profiles as DC arc plasma reached 850 C in less        than one second)    -   High heat and reactant transfer rates.    -   Smaller installation size for a given waste throughput    -   Melting of high temperature materials    -   Using of electricity as an energy source    -   Control of the processing environment through power supply.    -   More options for the process chemistry since the heating rate        can be easily controlled through electrical output in watts.    -   Higher sustainability since eliminating the usage of fossil        fuels.    -   Higher process controllability and smaller installation size.

A non-transferred arc plasma torch provides a plasma flow for treatingthe waste. The following formulas are shown below: (J. Heberlein, 2008).Specific enthalpy equation requires density, velocity and enthalpy asfunctions of the radial position r, R is the channel radius and {dotover (m)} is the total plasma gas flow rate.

$h_{ave} = \frac{2\; \pi {\int_{0}^{R}{\rho \; v\mspace{14mu} {hrdr}}}}{\overset{.}{m}}$

The average enthalpy can also be determined from an energy balance ofthe torch using the following equation. Were Q_(loss) I=the heat lostfrom the plasma torch.

{dot over (m)}h _(ave) =I*V−Q _(loss)

The average velocity can also be calculated from the following equation:

$v_{ave} = \frac{\overset{.}{m}}{{\rho ( T_{ave} )}A}$

m=mass of ions, I=plasma density, T_(ave)=Average Plasma temperature,and A=

Plasma Area.

2.6.1 Categorization of Thermal Plasma Systems

As more efficient and reliable torches for thermal plasma generationwhich acts as an alternative clean energy source of heat, have becomeavailable in recent years due to the development of the technology andthe utilization of plasma energy as an alternative energy source forpyrolysis/gasification. The technology main advantages involvesdelivering extremely high reaction temperatures up to 3000 C (L Tang,2013). Tdded to that, an ultra-fast reaction velocity compared totraditional pyrolysis gasification technology with great potential inplastic waste treatment. (L Tang, 2013). Since this is the chosen methodand focus for our Project, our design will involve focusing ondevelopment of Plasma Arc (DC) and (RF) and its implementation onreactor design that converts thermoplastic waste mixture to oil productsutilizing the highly efficient and reliable Plasma arc technology thatconverts thermoplastic waste to pure petroleum gas (ethane and methane)mainly and pure oil products which are illustrated in the figures. (ImJun Cho, 2015). It was also reported that oxygen in the reactor reducesthe yield of hydrocarbon gases and increases ash/tar which is theundesired product of pyrolysis and should be minimized to negligibleamounts. (Im Jun Cho, 2015)

Plasma pyrolysis system designs have been researched for more than halfa century, which has resulted in the availability of several designs atthe small and large scales. Below are useful parameters for differentparts of the pyrolysis process.

2.6.1.1 Plasma Arc Types

Plasma thermal generation can be achieved using a direct current (DC),an alternating current (AC) electrical charge, an RF (i.e. radiofrequency) induction or a microwave discharge (MW) explained below. (LTang, 2013). In our project we are focusing on DC (direct current) andRF (Radio frequency) plasma arc technology and its performance in thepyrolysis reaction which has operating temperatures in range of 450-600C. (Vasudeo, 2016)

2.6.1.2 Reactor Design Types

Plasma fixed or moving bed reactor system, plasma entrained-flow bedsystem, spout reactor system and spout-fluid reactor system designs. Thereactor design parameters will be feedstock volumetric flow rate,residence time, and end products to determine batch or continuousprocess system. (Don W. Green, 2008) (L Tang, 2013) The differentreactor designs illustrate techniques of heat transfer, heating duty andresidence time.

2.6.1.3 Plasma Working Gas Method

N₂ plasma system, Argon plasma system, H₂ plasma system, mixed gasplasma system, water steam plasma system, are inert gases and can beused as a medium of heat transportation to the liquid feedstock. (IgorA. Ignatyev, June 2014) Since Pyrolysis reaction occur in inert gas,high purity 99.99% N₂ gas is used in our experimental results. Nitrogenis also the most available and cheap inert gas thus is used in ourproject.

2.6.1.4 Thermal Plasma Pyrolysis Systems

Thermal plasma pyrolysis systems should be properly designed for energyefficient and cost-effective operations. The basic component of athermal plasma pyrolysis is the plasma generator (torch). The torch isthe source of thermal energy aimed at the reactants and can be generatedby various methods discussed below, including: DC/AC electric dischargesor transient arcs, RF and microwave discharges at near-atmosphericpressure, and laser-induced plasmas. (L Tang, 2013) Below are differentTypes of Plasma Arc Technologies. (L Tang, 2013). The Plasma sourcedelivers sufficient heat (Heat duty, KW) that is used for the pyrolysisreaction with a specific residence time specified between 30-45 minuteswithout catalyst.

2.6.1.4.1 DC (Direct Current) Arc Discharge

DC arc discharge provides a high energy density and high temperatureregion between two electrodes and, in the presence of a sufficientlyhigh gas flow, the plasma extends beyond one of the electrodes in theform of a plasma jet. The arc plasma generators can be divided intonon-transferred arc torch and transferred arc torch as shownschematically in FIGS. 2-6A and 2-6B respectively. DC plasma arc canreach up to 1300 C (L Tang, 2013). At our Laboratory experimentationusing simple DC Arc Plasma generates 800 C in less than 1 second whichis than the required temperature for pyrolysis reaction. Please refer toexperimental results for details.

The Arc Plasma Generators can be divided into non-transferred andtransferred arc torch. In non-transferred torch, the two electrodesdon't participate, in the processing and have only a function of plasmageneration. In a transferred arc reactor, the substance to be processedis placed in an electrically grounded metallic vessel and acts as theanode, hence this method is suitable only for reacting material which iselectrically conductive. (L Tang, 2013)

The average lifetime of electrodes ranges between 200 and 500 hours ofoperation under oxidative conditions. Normal power levels up to 1.5 MW.Scale-up is possible to 6 MW (Plasma Technology Research Centre, 2011).The majority of thermal plasma processes developed to date have used DCplasma generators due to the stable arcs that they can generate, howeverthis type of plasma generation is comparable and includes narrowpathways for gaseous materials. (L Tang, 2013)

2.6.4.2 RF (Radio Frequency) Plasma System

A radio frequency plasma system (an example of which is illustrated inFIG. 2-7) employs RF plasma torches that utilize inductive or capacitivecoupling to transfer electromagnetic energy from the RF power source tothe plasma working gas. The advantages of this plasma system includescompact design, extraordinarily high input energy per unit volume,ability of the RF plasma reactor to handle any chemical owing to theabsence of metal electrodes and a very long lifetime. RF plasmagenerators are commonly available at power levels of 100 kW and can bescaled to 1 MW range. (L Tang, 2013). RF frequencies are usually inrange of 10 MHz to 16 MHz. It is to be mentioned that RF plasma systemsoften utilize oscillator electronics which have inherently lowefficiencies. The RF Plasma experimental setup requires vacuumenvironment to work efficiently. (L Tang, 2013). The RF Plasma sourceused in the lab for the pyrolysis experiments is 13.56 MHz which is astandard plasma generation frequency for RF Plasma. (L Tang, 2013)

2.6.4.3 Microwave Plasma System

Microwave plasma systems are plasma systems that are created by theinjection of microwave power (i.e. electromagnetic radiation in thefrequency range of 300 MHz-10 GHz, typically 2.45 GHz; can in principlebe called “microwave induced plasmas”. An example of this is shown inFIG. 2-8. Microwave plasma operating pressure ranges from 0.1 Pa to 10Pa, In terms of power between a few Watts and several hundreds ofkWatts, sustained in both noble gases and molecular gases. (L Tang,2013)

Thermal Plasma are partially or strongly ionized gases, usually createdby electric arcs at atmospheric pressure. In fact, thermal plasmas canbe generated by many methods such as DC (direct current) electricaldischarges at current intensities higher than a few A and up to 10⁵ Åeither transferred arcs, or non-transferred plasma torches, AC ortransient arcs, pulsed arcs, RF and microwave discharges at nearatmospheric pressure. (Gleizes, 2005)

In thermal plasmas the electrons are mainly responsible for inelasticcollisions such as ionization, recombination, excitation, attachment anddetachment.

The electron temperature is equation to the ion temperature producing aplasma temperature (T_(plasma)) in range of 10⁶-10⁸. The factors beloware used in a plasma arc system design:

-   -   Ability to use not only inert active gases such as N₂, Air, CO₂        used as carrier plasma gases.    -   Sufficient long electrode life (typical 20-10,000 hour).    -   Ability to control gas enthalpy or heat transferred to the        treated material.    -   Energy efficiency and impulse power of the Thermal plasma        circuit.    -   The high specific heat flux at the cathode makes it a beneficial        component to select properly despite the higher losses at the        anode. The choice of cathode is determined by the plasma forming        gas and the specific enthalpy and should withstand the highest        number of hours to reduce maintenance work and increase        operations reliability.

2.6.2 Industrial Thermal Plasma Systems 2.6.2.1 Westinghouse PlasmaCorporation (WPC)

The Westinghouse plasma gasification technology has been in operationglobally for the past 10 years leading to successfully processedmultiple feed stocks including municipal solid waste, auto shredderresidue, sewage sludge and a variety of caustic hazardous materials. TheWestinghouse plasma gasification technology has three reference plantsand two commercial plants and illustrated below are the major processunits and technologies used in Westinghouse gasification plants.

A typical facility includes at least one continuously operatingpyrolysis reactor. Within the reactor the charge material exposed tovery high temperature profile which exits the top of the reactor throughtwo outlets. As stated below, here are the main process units atWestinghouse Thermal Plasma Pyrolysis Large Scale Treatment Facility:

-   -   Feed system: Received recyclable thermoplastic waste as        Feedstock to be processed, this stage involves feed elevator,        hopper, shredder and screw conveyer of feedstock waste to        prevent malfunction.    -   Particulate recycle system: Unprocessed feedstock after        gasification is recycled by transferring un-gasified plastic        waste to the Feedstock system.    -   Plasma gasification system: A slag removal system is installed        before the reactor. Plasma torches in a plasma gasifier        (reactor) provide thermal energy raising the Temperature to        cracking Temperatures producing syngas from thermoplastic waste.    -   Boiler: Produces LP, MP, and HP Steam which delivers the        required steam for steam turbine generator.    -   Gas clean-up system: A system in plasma gasification processes        aims to remove.    -   Thermal oxidizer: An air pollution control unit that decomposes        hazardous gases at a high temperature and releases them into the        atmosphere. (Process Engineering, 2014)    -   Steam turbine generator: Extracts thermal energy from        pressurized steam through rotating shafts.

2.7 Conclusion

In chapter 2, the main thermoplastic types are identified and theoperating conditions for thermoplastic pyrolysis reactions arecollected. Five main types of thermoplastics that form more than 90 wt %are LDPE, HDPE, PS, PP and PETE. The optimum operation temperatures are430-550 C, reaction residence of 30-45 minutes. The main products frompyrolysis reaction are hydrocarbon gases, liquids, wax and tar. Acondition of pyrolysis reactions is absence of oxygen and the mostcommonly used inert gas is nitrogen since it is abundant and economical.

Existence of PVC in thermoplastic feed stock causes negative effects dueto formation of HCl which is toxic, has a high reactivity with water,causes damage to metal structures. To address this, pretreatment at 320C of PVC feed stock can be used to remove chlorine ions. A CaO catalystbed can be used to remove chlorine ions at 320 C for any thermoplasticsthat have Cl ions in their chemical structure.

The heat duty required for pyrolysis can be calculated from specific andlatent heat capacity of individual plastics depending on the feed stockcomposition used in the pyrolysis reactor. The average heat dutyrequired is 1047 KJ/kg which is used in the thermal plasma heatcalculations.

Thermal plasma can be used in thermoplastic pyrolysis reaction using DC,RF or MW thermal plasma can be used and requires vacuum conditions tooperate effectively. Thermal plasma achieves better heat performance,and can be used for pyrolysis reactions 430-550 C temperature profileand temperature can be controlled through current thus providing bettercontrol characteristics, more sustainable technology and no harmfulgaseous emissions.

After the reaction residence time, gaseous products are condensedthrough a condensation system for collection of hydrocarbon liquids andwax. Tar is reduced by ensuring inert conditions to inhibit oxidation orcombustion of thermoplastics.

3. Methodology 3.1 Introduction

In order to convert thermoplastics to hydrocarbon gaseous and liquidproducts in a pyrolysis (oxygen starved environment) reactor, a 1 Lclosed system reactor of stainless steel 301L is set as the experimentalapparatus. In order to compare the effectiveness of the DC thermalplasma setup, a 220 V 4.8 A electric heater that raises the temperatureof a laboratory reactor to 550 C is used. The closed system reactor usescompressed gas (N2) to ensure pyrolysis environment. A stop watch isused for time monitoring and a K-Type thermocouple is inserted insidethe reactor few centimeters away from the thermoplastic sample tomonitor the temperature in Celsius scale per minute.

An initial sample of 15 grams of thermoplastic sheets are placed at theplastic holder and the reactor is filled with pure nitrogen gas througha compressed nitrogen cylinder and a regulator. The process of nitrogenfilling is repeated three times through inlet/outlet valves using avacuum pump that removes all air from the reactor vessel, then nitrogengas is pumped inside the reactor till pressure reaches 1 bar. The stepof placing the sample in the reactor may more broadly be referred to asplacing in a reactor an amount of thermoplastic to be converted. Thestep of using the vacuum pump to remove air from the reactor may morebroadly be referred to as depressurizing the reactor to remove air. Thestep of nitrogen filling may more broadly be referred to as filling thereactor with an inert gas.

The chosen reaction residence time is 30 minutes for both experiments(Experiment 1: Using electric heater Experiment 2 using: DC ThermalPlasma arc source). After the reaction is carried out for the residencetime K, the heating source is switched off and the gaseous productsescape the reactor system into a condensation system through a ballvalve. The liquid sample is collected and weighted. The step ofmaintaining the reaction for the 30 minute residence time may morebroadly be referred to as subjecting the amount of thermoplastic to athermal plasma arc source operating at a select temperature profile fora preselected residence time to produce a gaseous product. It will beunderstood that the residence time may be longer or shorter than the 30minutes used in the present disclosure. The step of the gaseous productsescaping the reactor system into a condensation system through a ballvalve may more broadly be referred to as directing the gaseous productthrough at least one condenser. The step of collecting and weighing theliquid sample may more broadly be referred to as collecting a liquidfraction condensed from the gaseous product in the at least onecondenser.

The process steps may alternatively be identified as follows:

receiving a feedstock of thermoplastic to be converted;

granulating the feedstock to reduce the thermoplastic to a preselectedgranule size (or otherwise size-reducing the feedstock to reduce thethermoplastic to a preselected particle size);

delivering the granulated feedstock to a preheat unit and preheating thegranulated feedstock based on a preselected preheat temperature profile;

delivering the preheated granulated feedstock into a reactor andsubjecting the feedstock to pyrolysis based on a preselected pyrolysistemperature profile for a preselected residence time to produce agaseous product;

directing the gaseous product through at least one condenser; and

collecting a liquid fraction condensed from the gaseous product in theat least one condenser.

In general, while granulating may be the preferred way to reduce theparticle size of the thermoplastic, other ways may be used.

The liquid product yield is calculated through the following equation:

${{Product}\mspace{14mu} {conversion}\mspace{14mu} {yield}} = \frac{{W\; \infty} - {Wi}}{W\; \infty}$

The initial thermoplastic sample is weighted using a mass scale, thehydrocarbon liquid yield produced and the product yield is calculatedfor the thermoplastic initial sample. The initial plastic sample ischosen to be 15 g for different types of thermoplastics including LDPE,HDPE, PS, PP and PETE.

The hydrocarbon liquid sample is then analyzed using a headspace gaschromatography analysis-with an FID (Flame Ionization Detector). The gaschromatography identifies the composition of the oil depending on theretention time which is matched to a retention time hydrocarbonidentification table and the carbon number of the hydrocarbon isidentified.

The same process is repeated for any thermoplastic sample collected fromboth experiments either electric heater or Direct current thermal plasmaheating source. The K-type thermocouple measures the temperature profileof the heating source of both experiments. The temperature profile withthe gas chromatography and product yield results can assess theperformance of direct current thermal plasma arcs to replace traditionalindustrial heating methods that is required for large scale productionpyrolysis reactors. The control experiment is to ensure same sample sizeis used for the initial thermoplastic used in both experiments. The 1Litre closed system reactor uses a vacuum pump to depressurize theclosed vessel system, and pure nitrogen gas fills the reactor. Theprocess is repeated three times to ensure that the reactor vessel iscompletely filled with nitrogen before switching on the thermal plasmasystem. The data is recorded and the thermal plasma system is assessedin terms of thermal efficiency, conversion rate. The oil products areanalyzed using the Gas chromatography results thus showing the chemicalcomposition of the produced oil and thus the thermoplastic mixturecomposition can be adapted to lead to a specific oil mixture compositionsuch as gasoline or diesel.

FIG. 3-1 is a thermal plasma circuit design flow chart.

3.2 Research Methodology Phases

The study was conducted into three phases which are discussed below:

Phase 1: Collection of operating conditions, reaction engineering,process operation related to thermoplastic pyrolysis to oil products.This phase also involves calculating the energy duty required forthermoplastics to convert to oil in inert conditions. Also, the reactionresidence time required and the various types of thermoplastics that canbe converted to oil products.

Phase 2: This phase aims to integrate direct current thermal plasma tobe utilized in pyrolysis reactor. The circuit is designed to achieve therequired heat duty in an experimental scale and to be able to work underthe pyrolysis reaction conditions in inert environments and achieve therequired high temperatures for 30 minutes. This stage involves carryingthermal plasma experiments in a vacuum vessel without a plasma sample.

Phase 3: This phase involves quantitative measurements includingtemperature profiles of thermal plasma during operation in a 1 Litrevessel. Also, hydrocarbon liquid products are analyzed using an FID GasChromatography and product yield is calculated. Life cycle cost analysisfor usage of thermal plasma against other heating methods areinvestigated.

3.3 Conclusion

Three phases are chosen for methodology, starting with detailed study ofthe process conditions, heat duty and applicable pressures andtemperatures needed for successful conversion of thermoplastics to oil.Phase 2 includes designed the thermal plasma circuit to comply with HSEstandards and achieve required heat duty needed for the pyrolysisreaction. Phase 3 will follow chart in FIG. 3-1 to ensure direct currentthermal plasma performance in the pyrolysis reaction. Phase 3 aims todesign a thermal plasma circuit that can achieve controllable hightemperature, operate in nitrogen environment and vacuum pressure.Hydrocarbon products are analyzed using gas chromatography and productyields are calculated.

The flow chart of the thermal plasma system methodology ensures ininitial design stages that the direct current thermal plasma can achievethe required heat duty and temperature profile. The thermal plasmacircuit is designed to comply with operating temperature and pressurerequired for the targeted residence time of 30 minutes. The circuit isdesigned to achieve controllable temperature through current input thusinhibiting runaway reactions. The plasma circuit is modified and adifferent plasma method is used in case conditions are not achieved.

The plasma circuit is tested in vacuum conditions to ensure safeoperations and a closed system vessel is used. After successful pressuretesting, a 15 g sample is used in the thermal plasma circuit.

4. Pyrolysis Reactions Process Analysis 4.1 Thermal Cracking OptimumTemperatures

In order to get good design temperatures for our thermal crackingprocess, analyzing thermoplastic waste mixture thermal cracking is abeneficial step to recommend an optimum design temperature. Severalthermal cracking experimentations have been investigated (Kyong-HwanLee, 2007). In comparison between 350 C and 400 C, thermal cracking at400 C showed better product yields which can be shown below in FIGS.4-1. (Kyong-Hwan Lee, 2007)

4.2 Activation Energy and Reaction Kinetics Measurements for PolymersPolystyrene:

The activation energy of polystyrene consumed in pyrolysis reactionsrange from 164 to 249 KJ mol−1. (Seung-Soo-Kim, 2004)

Propylene:

The activation energy of Propylene ranges from 208 to 288 KJ mol−1(Seung-Soo-Kim, 2004)

The Table below illustrates the kinetic parameters of selectedthermoplastics mixtures

Material E_(a) (KJmol−1) References Low Density Polyethylene 259.70 (J.Encinara, 2008) (LDPE) Polystyrene (PS) 164-249 (N. Wang, 2013)Polypropylene (PP) 208-288 (N. Wang, 2013) Polyethylene Tetraphalate235.7  (J. Encinara, 2008) (PETE) High Density Polyethylene 147.25 (S.M. Al-salem, 2010) (HDPE)

4.2.1. Reaction Rate Calculation Models 4.2.1.1. Temperature IndependentReaction Rate Equation (Simplified Model)

This section investigates the reaction kinetics related to pyrolysis ofthermoplastic waste mixtures. The methods elaborated will help us in thedesign stage to final the rate of products over rate of reactants. Thefollowing rate of reaction definitions are all interrelated and allintensive rather than extensive measures. (Levenspiel, 1999). Thefollowing is a basic explanation of reaction rate in terms of componenti. The rate of change in numbers of moles of this component due to thereaction rate dNi/dt, then the rate of reaction in its various forms isdefined as follows:

Based on Unit Volume of Reacting Fluid:

$r_{i} = {{\frac{1}{V}\frac{{dN}_{i}}{dt}} = {\frac{{moles}\mspace{14mu} {of}\mspace{14mu} i\mspace{14mu} {formed}}{( {{volume}\mspace{14mu} {of}\mspace{14mu} {fluid}} )({time})}( {{Levenspiel},1999} )}}$

It will be noted that the reaction rate varies from a reaction to otherwhich decides the type of the reactor to be chosen either Batch reactor,Semi-batch reactor, continuous—stirred Tank reactor or a plug flowreactor (PFR) (Sinnott, 2005). The method explained above is a verysimple method to determine the rate of reaction from moles of productsformed per unit time.

The following conversion X equation is defined as follows:

$X = \frac{W_{i}}{W_{0} - W_{\infty}}$

X=Mass Conversion, Wo=Mass of oil product, Wi=initial mass sample, andW∞=Final Mass sample.

4.2.1.2. Reaction Kinetics of Pyrolysis Reactions

Following this kinetic study (Paul T. Williams, 2006), a pyrolysispressure reactor at an initial nitrogen pressure of 0.2 MPa generating amaximum of 10 MPa pressure at elevated pyrolysis temperature of 500 C.The following table shown below, shows the reaction simulated massfractions of different thermoplastics by weight proportions.

Plastic Proportion (wt %) Polyethylene (HDPE) 44.4 Polypropylene (PP)21.2 Polystyrene (PS) 13.3 Polyvinyl chloride (PVC) 12.2 Polyethylenetetraphalate (PETE) 8.9

Below is a Table explaining the pyrolysis product yields of plasticwastes produced from the mixture mentioned above:

Hydrocarbon Residue Plastic waste Oil (wt %) gas (wt %) (wt %) Pyrolysis(Nitrogen) 48.7 3.7 34.6

The results showed that existence of paper and dirt in the feed sample(reactant) also reduces the Oil and Hydrocarbon Gas and produces a veryhigh percentage of residue/tar is produced. Therefore, it is vital toensure that all the mixture plastic mixture is free from paper or dirtto ensure the profitability and high product yield of oil andhydrocarbon. Thermoplastics can be separated easily from MSW usingcommercially available density-based separation methods. (G. Dodbiba,2002)

It was also noted that oil products produced from pyrolysis had a highconcentration of alkanes and single aromatic compounds which will beinvestigated in experimentation. (Paul T. Williams, 2006) Product yieldsfrom individual plastics pyrolysis are shown in FIG. 4-2.

4.2.2. Achieving Heavy Oils or Gaseous Oil Products at DifferentOperating Conditions

Referring to (Kastner H. and Kaminsky, 1995), thermal cracking ofpolyethylene in a fixed bed reactor over temperature ranges less than550 C, high yields of useful products such as heavy, liquid oil wereachieved. Changing the reaction temperatures to above 550 C yields moregaseous products and aromatics due to more secondary reactions ofaromatics above that temperature. (Kastner H. and Kaminsky, 1995)(Prakash K, 1997). Another reaction kinetic study, according to (S. M.AI-salem, 2010), the following is a calorific Value of some majorplastics compared with common fuels.

Item Calorific Value (MJ Kg−1) Polyethylene (PE) 43.3-46.5Polypropylene(PP) 46.50 Polystyrene(PS) 41.90 Kerosene 46.50 Gas Oil45.20 Heavy Oil 42.50 Petroleum 42.5 

Another study showed the reaction kinetics of pyrolysis reactions, thefollowing two equations calculate the activation energies of crackingreactions and mass conversion with time in the reaction. The equationbelow can be used to develop reaction rate.

${- \frac{dW}{dt}} = {{{k \times {W^{n}( {{N.\mspace{14mu} {Miskolxzi}},2012} )}} - \frac{dW}{dt}} = {{Reactant}\mspace{14mu} {mass}\mspace{14mu} {loss}\mspace{14mu} {per}\mspace{14mu} {unit}\mspace{14mu} {time}}}$

n is the reaction order n=1 for pyrolysis, W=Initial Weight of Sample,A₀=pre exponential factor, c=conversion factor

$c = \frac{Wo}{W}$

Activation energies were calculated by using the Arrhenius equation.

$k = {{Ao}\mspace{14mu} {\exp ( {- \frac{Ea}{RT}} )}}$

According to experimental trials and publication (N. Miskolczi, 2012),below are values of k. reaction Rate has units of mol dm⁻³ s⁻¹.

Reaction Temperature 410 C. 430 C. 450 C. (Rate Constant K found Sampleexperimentally) Polyethylene (PE) 0.00253 0.00771 0.03762 Polypropylene(PP) 0.00922 0.01590 0.04971

4.2.3. Reaction Products and Temperature Profiles of Thermoplastics

According to one of the main handbooks in Plastic Recycling, (JoséAguado, 1999) there are four Main Product fractions expected fromrecovering of plastic feedstock recycling through pyrolysis (i.e.thermal degradation in inert conditions) which are gases, oils, solidwaxes and a solid residue. As the Temperature is increased, the amountof gases, the fraction of gases also increases and the solid residueappears as a solid char due to the enhancement of hydrocarbon cokingreactions. There are three different decomposition pathways forpyrolysis of plastic feedstock recycling:

Random scission at any point in the polymer backbone leading to theformation of smaller polymeric fragments as primary products.

End-chain scission, where a small molecule and a long-chain polymericfragment are formed.

Abstraction of functional substituents to form small molecules.

The most common pathways occur simultaneously. For PE polyethylene andPP polypropylene thermal degradation occur by both random and end-chainscissions. In the case of PVC, however, the predominant mechanism of thefirst step is the removal of HCl to avoid chloride ions during pyrolysiswhich change the PH and damage the reactor vessel followed by normalpyrolysis reaction similar to other thermoplastics. (D. P, 1999).

Polymer thermal decomposition is an endothermic process that involvesthe dissociation of the C—C bond thus breaking down the polymer intouseful oil products. FIG. 4-3 is a direct relationship between thedissociation energy and the decomposition temperature for differentpolymers.

FIG. 4-4 shows the pyrolysis reactions that occur in thermoplasticpolymer cracking.

As shown in FIG. 4-4, the following reactions occur in thermoplasticpyrolysis of polymers (José Aguado, 1999)

-   -   Initiation, involving the scission of the first bonds in the        chain yielding two radicals, which may occur at random or        end-chain positions.    -   Depropagation, including the release of olefinic monomeric        fragments from primary radicals.    -   Hydrogen chain transfer reactions, which may occur as        intermolecular or intramolecular processes.    -   P-Cleavage of secondary radicals to yield an end-chain olefinic        group and a primary radical.    -   Formation of branches by the interaction between two secondary        radicals or between a secondary and a primary radical.    -   Termination, which takes place either in a bimolecular mode,        involving the coupling of two primary radicals, or by        disproportionation of the primary macro radicals.

4.3. Thermal Conversion of Individual and Mixture Plastics

This section discusses in details aspects of the thermal conversion ofindividual polymers which are the main components of plastic wastestream such as polyethylene, polystyrene, PVC, and PETE. This sessionfocuses on the mechanistic and kinetic factors as well as type ofproducts derived from thermal decomposition of each individual polymer.

4.3.1. Polyethylene

Polyethylene is the major polymer present in plastic wastes. Both lowdensity and high density polyethylene are found in large quantities inplastic residues. HDPE is a highly linear polymer, whereas LDPEpossesses a certain degree of branching. (D. P, 1999) HDPE exhibits ahigher crystallinity and a higher crystalline melting point than LDPE,due linear chains of LDPE can be more closely packed the polyolefin arecompletely volatilized at temperatures below 500 C which can also benoticed in FIG. 4-5.

Referring to FIG. 4-6, it can be seen that optimum operating conditionsfor HDPE is around 447 C and for LDPE around 417 C. The main productsobserved in the gaseous effluent from the pyrolysis reactor weremethane, ethane, ethylene, propane, propylene, acetylene, butane,butene, pentane, benzene, toluene, xylene and styrene. At the lowesttemperatures investigated (450 and 550 C), significant amounts of tarsand waxes were detected in addition to gaseous products. It was observedthat the more branched polyethylene yielded more aromatic compounds.(José Aguado, 1999) therefore, LDPE yield more aromatic compounds thanother unbranched polymers.

4.3.2. Polypropylene

Polypropylene is a polyolefin found in high concentrations in theplastic waste stream. Compared to PE, the backbone of the PP molecule ischaracterized by the presence of a side methyl group at every secondcarbon. Random chain scission of polypropylene produces both primary andsecondary radicals. Subsequently, tertiary radicals are formed byintramolecular radical transfer reactions. This fact implies that halfof the carbons in a PP chain are tertiary carbons and so, as aconsequence of their higher reactivity, PP is thermally degraded at afaster rate than PE which can be noticed in FIG. 4-7 below, which showsthat pyrolysis occurs at much lower temperatures than PE. The optimumoperating temperature for a PP Polymer pyrolysis reactor is 407 C.

4.3.3. Polystyrene

Polystyrene plastics constitute a significant part of industrial andhousehold wastes. As in the case of polypropylene, half of the carbonsin the polystyrene chain are tertiary due to the presence of sidebenzylic groups. (Jose Aguado, 1999) Therefore, thermal PS pyrolysisalso occurs at relatively low temperatures in range of 350 C using a GCand TG analysis with higher intensity at 420 C (FIG. 4-8). It is also tobe noted that the major product obtained is the starting monomer. Thisfact is valid for both low and high temperature degradation. Therefore,PS is one of the few polymers that can be thermally depolymerized. Mainstable products reported were Toluene, ethylbenzene, cumene, tri-phenylbenzene, a-methyl-styrene, diphenyl-propane and diphenyl butane. (JoséAguado, 1999)

4.3.4. Polyvinyl Chloride

Polyvinyl chloride is a polymer with a wide range of commercialapplications. However, its use has been the subject of great controversyin recent years due to its high chlorine content. (D. P, 1999)Approximately 56 wt % of the polymer is HCl, which is released atrelatively low temperatures, creating toxic and corrosive conditionssuch Cl-ions need to be separated before pyrolysis reaction.

HCl can be removed at low temperature in range of 200-360 C thermaldecomposition of PVC is recommended in a two-step process. Step 1,dehydrochlorination of the polymer to form a polyene macromolecularstructure followed by cracking and decomposition of the polyene atelevated temperatures above 375 C (see FIG. 4-9).

4.3.5. Polyethylene Tetraphalate PETE

Pyrolysis experiments in Inert gases showed show a peak around 420 Cwhereas 82% of the initial mass is volatilized up to 500 C. The productsreleased were a complex mixture composed mainly of acetaldehyde, benzoicacid, ethyl-benzoate and vinyl-benzoate. (José Aguado, 1999). Williamsand Williams have investigated PETE pyrolysis up to 700 C in a fixed bedreactor, three fractions being collected: gases, oil and char. Gases andoil accounted for about 80% of the starting polymer mass. The gases weremainly carbon dioxide, due to the presence of oxygen in the PETmacromolecules, although minor amounts of methane and ethylene were alsodetected. (Williams, 1997)

4.3.6. Thermal Conversion Of Mixture Plastics

In this section, Conversion of complex Thermoplastic waste mixtures ofseveral types of plastic, which is the case when processing realmunicipal plastic wastes are discussed. (José Aguado, 1999) This sectionwill highlight technical factors such as descriptions of reactors andprocesses, pretreatments for mixed plastic wastes as well as possibleinteractions which may occur when several plastics are simultaneouslydegraded. Pyrolysis of thermoplastic mixtures yield different results incomparison with individual plastics due to polymer chain interaction.

4.3.6.1. Activation Energy Measurements for Plastic Mixtures

Activation Energies are a vital measurement for reaction kinetics ofmolten plastic waste to pure oil products. Below are the activationenergy and Arrhenius exponential factors of different types of polymers.(J. F. Gonzalez, 2008) These values can be calculated to find theestimated energy needed to achieve pyrolysis reaction either in processsimulation or expected heat duty and rate of reaction needed.

Plastic Type Ea (KJ mol⁻¹) K₀, s⁻¹ Polystyrene (PS) 136.64 1.61 × 108Low Density polyethylene (LDPE) 118.31 6.97 × 108 PolyethyleneTetraphalate (PETE) 161.23 3.85 × 109 Polypropylene (PP) 169.35  1.06 ×1010 Recycled Plastics (RP) 210.35  3.5 × 1012

5. Proposed Thermal Plasma System

Plasma is a quasi-neutral ionized gas assumed to be in thermalequilibrium, using the following equation known as Saha-Langmuirequation that relates the ionization state of an element to temperatureand pressure. The equation can be used to estimate the amount ofionization is to be expected in a gas, assuming thermal equilibrium.

$\frac{n_{n}}{n_{n}} = {2.4*10^{21}*\frac{T^{\frac{3}{2}}}{n_{i}}*e^{- {(\frac{Ui}{KT})}}}$

n_(i) and n_(n) are the ion and neutral atom density respectively. T isthe gas temperature in degree kelvin

K Boltzmann constant

Ui ionization energy required to strip one electron from an atom

Another equation that is used that compute average energy density, using

Maxwellian distribution:

$E_{avg} = \frac{\int{( \frac{1}{2} )*m*U^{2}*{F(u)}*{du}}}{\int{{F(u)}*{du}}}$

E_(avg)=½ KT per degree freedomU²=Kinetic energy of the particlesF (u)=Number of particles per m³ with velocity between U and U+duM=average mass of particlesAdded to that, thermal motions generate pressure thus the followingequation relates pressure and temperature:

P=n*KT

P=Particle pressuren=Particle Density

K=Boltzmann Constant

T=absolute Temperature

FIG. 5-1 is a diagram categorization of mechanical and electricalcomponents needed for the thermal plasma circuit implementation inpyrolysis reactors.

As seen in FIG. 5-2, a 270 W Thermal plasma operating in vacuum pressureof −0.95 bar using non-transferred direct current with ceramic nozzlesetup to stand high temperature emission of plasma ions.

The plasma temperature reaches in a fraction of a second 890 C which isa much higher temperature than the required operation temperatures ofthermoplastic to oil pyrolysis reactions.

FIG. 5-3 shows a direct current thermal plasma jet in vacuum chamber.FIG. 5-4 is a direct plasma generation over a ceramic nozzle. FIG. 5-5shows a direct thermal plasma temperature 890 C using K-Typethermocouple.

The plasma emission is used to be directed over a thermoplastic holderof 15 g of LDPE in nitrogen atmosphere at vacuum pressure of −0.95 bar.The plasma emission is allowed to work for thermoplastic pyrolysisreaction time of 30 minutes and switched off before gaseous products arereleased to the condensation system.

In the designed experiment direct current non-transferred circuit of9000 V, 30 mA current at frequency 60 Hz. The circuit includescapacitors, Ceramic plates, Diode, and resistors. The Input power sourceof the thermal plasma circuit is AC (alternating current) and the outputimpulse power is DC as shown in FIG. 5-6.

5.1.1. Capacitors calculations

C=1500 PF

Vc=3 KV

V_(T)=9 KV

C_(TOTAL)=1000 PF

R_(C)=1Ω

L=1000 nH

As shown below, C stands for capacitors, each of which has 1500 PF intwo loops connected in parallel to a diode that restricts the current topass to the capacitors which store the electric energy,

As seen above, the thermal plasma circuit, has three capacitors inseries each capacitor with 1500 PF, Pico Farad.

$\frac{1}{C_{T}} = \frac{1}{\frac{1}{C_{1}} + \frac{1}{C_{2}} + \frac{1}{C_{3}}}$

Thus total capacitance in the parallel loops is 1000 pF or 1 nF.

5.1.2. Half Wave Rectifier

With reference to FIG. 5-7A, the function of the diode is to convert thealternating current to direct current for thermal plasma generationcreating a half wave rectifier as shown. A half cycle is used to chargethe capacitors, and in the response time of absence of current (see FIG.5-7B), the capacitors release the charge load at the electrodesgenerating a thermal plasma torch at vacuum operating pressure −0.95bar.

The equations used to calculate the total voltage, current and othercorrelations are shown below:

$V_{T} = {{\frac{1}{C_{Total}}{q(t)}} + {{Rc}\frac{- {dq}}{dt}} + {L\frac{d^{2}q}{{dt}^{2}}}}$

Thermal plasma pulse power can be calculated as

I _(max) ×V _(max)

I_(max)=30 mA, V_(max)=9000V

Thus impulse power for plasma generation is calculated as below: Impulsepower used P_(impulse): 270 W.

5.2. Conclusion

The thermal plasma circuit includes a diode that converts AC powersupply to half wave rectifier and total capacitance in the circuit is 1nF. A half wave rectifier is created, in presence of current half cycle,the capacitors are charged, while in absence of current, the charge isreleased and thermal plasma discharge is created. A K-type thermocoupleshows 625.6 C as an initial temperature and maximum temperature of 890 Cis achieved.

6. Thermoplastic Reaction Experiment

The laboratory experimental setup aims to convert thermoplastic waste tooil products in nitrogen conditions at atmospheric and vacuum pressuressince thermal plasma operates best at vacuum pressures. Sophisticatedlaboratory equipment were purchased and the following experimental setupwere developed aiming to convert single thermoplastics as well asmixture components of LDPE, HDPE, PETE, PP and PS materials. FIG. 6-1 isa schematic diagram of an example of an experimental setup.

6.1. Equipment Overview

Equipment used is described below:

6.1.1. Pure Nitrogen Gas Cylinder

An Air Liquide™ compressed Pure nitrogen cylinder (4.5 Nm3 99.99% purenitrogen) is purchased for pyrolysis and thermal plasma operations. Thenitrogen cylinder emits pure nitrogen gas through a regulator emitingnitrogen at 2 bar inside the closed vessel operated by V-2. All othervalves should be closed and V-2 opened before allowing nitrogen gas toflow to reactor. The vessel is filled with nitrogen till pressureincreases from −0.95 bar to 1 bar. The process is repeated 3 times(vacuum-nitrogen filling) till the vessel is made sure to be mostlynitrogen. It is to be noted that vacuum pump and nitrogen filling isoperated separately to avoid gas leaking.

6.1.2. Condensation System Operations

After the reaction residence time of 30 minutes, the gaseous productsare expected to be hydrocarbon gases and liquids. The thermal plasmasystem is switched off, and valve V-3 is opened to allow gaseousproducts to pass through the condensation system. The condensationsystem runs tap water at 25 C in a continuous cycle. Condensation systemonly operates after the reaction residence time is achieved for 30minutes. The heating source is switched off, pressure is changed toatmospheric and gaseous products are allowed to condense through thecondensation system. The gaseous hydrocarbons condense to light oil,diesel and wax into the oil collector.

6.1.3. K-Type Thermocouple

A K-Type thermocouple is inserted inside the closed vessel attached tothe heating source to get a temperature/time profile. The thermocouplehas an initial temperature of 23.5 C before starting the experiment, thetemperature profile is measured per minutes of 30 minutes and theperformance is compared with the thermal plasma experiment.

6.1.4. DC Thermal Plasma and Electric Heater Heating Sources

In experiment 1, a ceramic electric heater is used as a heating sourcefor the thermoplastic pyrolysis reaction, while in experiment 2, thermalplasma is used as the heating source on a 15 g LDPE sample and atemperature profile as well as hydrocarbon products are collected andanalyzed. In experiment 2, the electric heater is used without thethermal plasma setup.

Both experiments are carried out in the same closed system to ensuresimilar parameters. Temperature profiles are recorded as well aselectric consumption and product yields.

6.2. Experimental Setup 6.2.1. Thermal Plasma Experiment

The direct current thermal plasma circuit was tested in a vacuum chamberfor 30 minutes including a k-type thermocouple to measure plasmatemperature on a 15 g plastic sample. The pyrolysis reactor vessel is a1L stainless steel vacuum chamber. The setup is shown in FIG. 6-2.

As shown above, a thermal vacuum chamber (1 L) is used to demonstrate anon-transferred DC thermal plasma source that releases heat on a plasticholder. The system operates in vacuum till reaction residence time isachieved.

FIG. 6-3 shows DC thermal Plasma emissions on a 15 g LDPE sample. Thethermal plasma arc is switched on, on a 15 g thermoplastic sample for areaction residence time 30 minutes and the temperature profile isrecorded. After 30 minutes, the gaseous products are allowed to escapeout of the reactor and into the condensation system. FIG. 6-4 showsthermal plasma emission through direct current ceramic nozzle setup.

At around 230 C, as shown in FIG. 6-5, the thermoplastics start tochange to a molten state before reaching pyrolysis temperatures.

As seen in FIG. 6-6, the direct current thermal plasma emission meltsthe LDPE plastic sample and reduces in size after few seconds, to checkthe temperature profile please refer to results section.

6.3. Thermoplastic Pyrolysis Using an Electric Ceramic Heater

In order to compare the performance of the direct current thermalplasma, the pyrolysis experiment is carried out using a laboratory ColeParmer™ electric heater consuming electrical energy 1058 W and can reachup to 550 C as shown in FIG. 6-7.

After the reaction residence time, the gaseous products are allowed toescape at atmospheric pressure through a condensation system thuscondensing liquid hydrocarbons and waxes. FIG. 6-8 shows the release ofgaseous products through a condensation system.

6.4. Laboratory Health, Safety and Environmental Regulations 6.4.1.Compressed Nitrogen Gas Handling

The use of compressed gases should protect the users and can be achievedby safe storage, proper gas handing and operations, and taking thenecessary precautions when dealing with pressurized cylinders, and usageof appropriate cylinder regulators. (O. Karl, 2006). Complying with OSHAstandards 29 CFR 1910.1200. (PraxAir, August 2013)

The expected potential health effects, are as follows:

6.4.1.1. Effect of a Single Acute Over Exposure

Inhalation: Asphyxiant. Effects are due to lack of oxygen. Moderateconcentrations may cause headache, dizziness, excitation, vomiting andat maximum exposure could cause death due to suffocation.

Skin Contact: No harm expected.

Eye contact: No harm expected.

Effects of Repeated (Chronic) over exposure: No harm expected.

6.4.1.2. First Aid Measures

Inhalation: Remove to fresh Air. If not breathing give artificialrespiration. If breathing is difficult, qualified person may giveoxygen.

Skin Contact: An unlikely route of exposure. This product is a gas atnormal temperature and pressure.

Eye Contact: An unlikely route of exposure. This product is a gas atnormal temperature and pressure. (PraxAir, August 2013)

6.4.2. Thermal Plasma Handling

Thermal plasma can achieve very high temperatures and specialprecautions need to be taken for safety and health standards. (O. P.Solonenko, 2003) Thermal plasma temperatures can reach up to 5000 C andthe chosen high temperature limit for the experiment is 1000 C.Measurements taken in case of higher temperature detected using K-Typethermocouple:

-   -   Switching off main power supply.    -   Pressure Test before switching on the thermal plasma system to        prevent leaks during operations.    -   Ensure pressure is below atmospheric for optimum plasma        operations.

6.5. Conclusion

A closed system vacuum chamber that operates under −0.95 bar usingnitrogen gas to achieve inert conditions required by pyrolysis reaction.A 270 W direct current non-transferred thermal plasma is compared to a1056 W electric heater in pyrolysis reaction of a 15 g LDPE and a 30minute reaction time. A k-type thermocouple is used to measure thetemperature per minute of the two heating source systems while thegaseous products are passed through a condensation system after thereaction time. The collected samples are used to calculate productyields and pyrolysis oil is analyzed using flame ionized detector gaschromatography.

7. Experimental Results 7.1 Temperature Profiles

FIG. 7-1 shows temperature profiles which were recorded using the K-Typethermocouple for the Direct Current thermal plasma system (30 mA, 9000V, 270 W) in comparison to a laboratory electric heater that uses (4.8Å, 220 V, 1056 W). As seen in FIG. 7-1, the direct current thermalplasma has a higher and better temperature performance on the 15 gthermoplastic sample and can be easily controlled by the input currentto the plasma circuit. It can also be noted that the DC thermal plasmawith 240 W can achieve higher temperatures than needed by the pyrolysisand can achieve up to 860 C.

Below are the computed temperature profiles computed per minute:

Time (minute) 1 2 3 4 5 10 15 20 25 30 Pyrolysis 79 163 260 340 420 6282 92 507.2 540 Electric Heater Pyrolysis 625.6 756.8 758.7 762.3 769.395 28.3 37.1 45 860 Thermal Plasma

7.2. Gas Chromatography Results

The gaseous products from the pyrolysis experiment pass through acondensation system and the volatile oil sample is collected andanalyzed using Gas chromatography. FIG. 7-2 shows the oil samplecollected from a 15 g sample of LDPE.

In order to collect the maximum amount of liquid oil products from theplastic sample, after 20 minutes, the gaseous products are allowed toenter a closed condensation system and the liquid products are collectedin a flask as shown in FIG. 7-3. The gaseous products are allowed tocondense at 25 C using potable cooling water.

7.2.1. Headspace Gas Chromatography Analysis—with an FID (FlameIonization Detector)

The oil sample was analyzed using a headspace gas chromatography usingmethanol flame ionization detector. The oil sample showed the existenceof the following hydrocarbon compounds:

1,4, dichlorobenzene

N-butyl benzene

Undecane (Sur)

In FIG. 7-4, a different GC method with FID, shows the existence of thefollowing hydrocarbon compounds:

C10 (decane)

C16

C34

In FIG. 7-5, GC Analysis with FID shows the existence of C10, C16 andC34 compounds in the pyrolysis oil which shows heavy hydrocarboncompounds existence in the oil sample collected from the pyrolysisexperiment.

The analysis of the pyrolysis oil is shown in the following table:

Parameter Result Units 1,4-dichlorobenzene-d4 (Surr) 87.9 μg/g Benzene0.008 μg/g Ethylbenzene 0.041 μg/g F1 (C6-C10)-Less BTEX 61.8 μg/g F1(C6-C10) Incl. BTEX 62.4 μg/g p-Xylene 0.098 μg/g o-Xylene 0.183 μg/gToluene 0.271 μg/g Total Xylenes 0.281 μg/g undecane (Surr) 134 μg/g F2(C10-C16) 2340 μg/g F3 (C16-C34) 685 μg/g F4 (C34-C50) <10 μg/g

The data displayed in μg/g and shows existence of 1-4 dichlorobenzene insmall quantity, minor percentages of benzene, ethylbenzene. In terms ofhydrocarbon analysis (C10-C16) shows the highest concentration of 2340μg/g, followed by existence of C16-C34 and small traces of heavierhydrocarbon content of C34-50.

7.3. Pyrolysis Gas Ignition Test

The pyrolysis hydrocarbon gases that was emitted in the reaction (C1-C4)was tested for ignition to ensure existence of methane or petroleumgases. The ignition test was using an ignition sparker and showedignition capability thus showing the existence of flammable componentsas shown in the FIG. 7-6.

7.3.1 Product Yield Results

As mentioned earlier, the expected products from a thermoplasticpyrolysis reactions are hydrocarbon gases, oil, wax and tar. Existenceof pure nitrogen gas reduces the tar which is an undesired product inour reaction. The product yield results use the following equation tocalculate yield in terms of mass:

$X = \frac{W}{W_{0} - W_{\infty}}$

X=Mass Conversion, Wo=Mass of product oil, Wi=initial mass sample,W+=final mass sample.

The initial thermoplastic sample weight, Wo is measured using a massscale and placed inside the reactor. The final tar and wax sample ismeasured which is W∞ and considered undesired product. The conversion Xis the successful conversion of thermoplastic waste to oil productswhich is the desired product. Below are the results from a 15 g LDPEsample.

Material Weight (g) LDPE (Reactant) 15 g Pyrolysis Oil Volume 7 mL (8.54g) Density 1.22 g/cm3 X (Conversion Rate) 0.569 (56.9%)

FIG. 7-7 shows the products obtained from thermoplastic conversion ofLDPE in a 30 minutes pyrolysis reaction under 550 C.

After the reactant is placed, a vacuum pump is used to reduce pressureto −0.95 bar and nitrogen gas is pressurized inside the vessel, theprocess is repeated multiple times to ensure inert conditions (N2 gas)for the pyrolysis reaction. Samples were collected of hydrocarbon oil,wax and tar as shown FIG. 7-8. With reference to FIG. 7-9, 7 mLpyrolysis oil calculated from 15 g of LDPE in a pyrolysis reaction.

7.4. Conclusion

A 240 W direct current thermal plasma circuit showed higher temperatureperformance against 1056 W electric heater and achieved more thanpyrolysis temperatures needed 550 C on a 15 g LDPE thermoplastic sample.15 mL were produced from a 15 g LDPE thermoplastic sample under vacuumpressure of −0.95 bar, operating temperature of 550 C and reactionresidence time of 30 minutes. The pyrolysis oil produced were analyzedusing a FID gas chromatography that showed existence of ethylbenzene anddecane.

Toluene and Xylene chemical components were also found in the pyrolysisoil produced.

Product Yield achieved using the mentioned conditions are 60 wt % topure oil products. Hydrocarbon gases released were tested for ignitionand showed high ignition characteristics. Tar is reduced by ensuringreaction occurs in nitrogen conditions through the usage of nitrogenpressurized gas.

8. Large Scale Plastic to Oil Pyrolysis Process Design

Development of a new chemical plant or process from concept evaluationto profitable reality is often an enormously complex problem. Aplant-design project moves to completion through a series of engineeringstages such as is shown in the following:

1. Inception

2. Preliminary evaluation of economics and market3. Development of data necessary for final design4. Final economic evaluation5. Detailed engineering design

6. Procurement 7. Erection

8. Startup and trial runs

8. Production 8.1. Conceptual and Preliminary Plant Design

Constraints of a design such as those that arise from physical laws, andthermodynamics of the feed or reactants. Within this boundary there willbe a number of plausible designs bounded by the other constraints, theinternal constraints, over which the designer has some control such as,choice of process, choice of process conditions, materials, andequipment.

Economic considerations are obviously a major constraint on anyengineering design, since plants must make a profit. (Sinnott, 2005).During the conceptual design phase, the target of the project may bedefined and an optimum process is designed based on this information.The following points need to be achieved during the conceptual designstage:

-   -   Mass and energy balances    -   Process simulation (e.g. with Aspen Plus®)    -   Process selection    -   Evaluation and comparison of design options    -   Plant layout—The design work required in a chemical engineering        plant can be divided into two phases:

Phase 1: Process Design

This covers the steps including initial selection of the process to beused, through Process Flowsheets, reaction path selection,specification, and chemical engineering design equipment. This followsby Process Flow diagram and Piping and Instrumentation (P&ID) Diagram.

Phase 2: Plant Design

Detailed mechanical design of equipment including the detailedmechanical design of equipment, structural, civil, and electricaldesign; and the specification and design of the ancillary services. Asseen FIG. 8-1 is the detailed structure of a chemical engineeringproject.

8.2. Plastic to Oil Conceptual Design Engineering Project

Plant Design Basis: Processing Thermoplastic waste feed at 10tonnes/hour to pure oil products including LPG, gasoline, diesel, waxand tar production. The expected annual production for this plant is87.6 KTA (Kilo tonne per annum). The following are the major processsteps in the thermoplastic to oil plants.

8.2.1. Municipal Plastic Waste Granulation

The pyrolysis chemical plant aims to convert thermoplastic feed fromMunicipal waste of Ontario through a series of chemical and physicalprocesses to oil products. A unit that can be used in large scalepyrolysis plants is the granulation process chosen to be Unit 1. Itincludes mechanical equipment for granulation that reduce the size ofsolid plastic waste in order to increase the heat transfer surface areaand heat transfer properties during preheating stage. Particle sizediameter is a parameter in granulators. The PSD chosen is set to be 6-8mm.

8.2.2. Thermoplastic Preheating to Molten Plastic

This unit receives granulated thermoplastic waste in agitated tanks werePre-heating is applied to molten solid thermoplastic waste mixture toliquid state. The feed temperature to this system is around 30 C and theexit temperature is 250 C to ensure that all the thermoplastic waste isin liquid state. This Unit prepares the thermoplastic waste for thermalcracking to oil products and prevents agglomeration of solid plasticsinside the pyrolysis reactor. (Sinnott, 2005)

8.2.3. Pyrolysis of Molten Thermoplastic Waste to Oil Products

This stage involves Thermal cracking or pyrolysis at elevatedTemperatures of up to 450 C-540 C in inert conditions. The optimumTemperature is determined the feed stock thermoplastic composition. Thechosen residence time of the pyrolysis reactor is 30 minutes and gaseousproducts are allowed to enter a condensation system and gaseous productscondense to hydrocarbon liquids.

8.2.4. Wax and Tar Removal

Removal of Wax, tar and solids from the system to avoid clogging andpoor heat transfer since plastics are poor conductors of heat.Therefore, ash, tar and wax need to be removed continuously from thepyrolysis reactor system which is removed from the bottom of the reactorusing valves.

8.2.5. Light Oil and heavy Separation Units

This stage involves separation of oil products, coke and tar removal,condensers, vessels and separation tanks. The condensation systemreduces temperatures using flash separators to condense gaseous productsfrom 550 C to 30 C and can be used as an energy recovery to heat coldstreams.

8.2.6. Storage of Hydrocarbon Fuels

This unit includes storage tanks that store End-Product hydrocarbonfuels at atmospheric pressure that ensures safe storage at atmospherictemperature for a storage capacity for 15-30 days depending.

8.2.7. Design Factor (Design Margins)

Experienced designers include a degree of over-design known as a “designfactor, design margin, or safety factor, to ensure that the design thatis built meets product specifications and operates safely. Designfactors are also applied in process design to give some tolerance in thedesign. For example, the process stream average flows calculated frommaterial balances are usually increased by a factor, typically 10%, togive some flexibility in process operation. This factor will set themaximum flows for equipment, instrumentation, and piping design. Designfactors can be mentioned in drawings, calculation sheets, and manuals.

8.3. Process Block Diagram (PBD) and Process Flow diagram (PFD)

A block diagram is the simplest form of presentation. Each block canrepresent a single piece of equipment or a complete stage of a process.It shows the principle stages of a process including separators,reactors, vessels, heat exchangers, vessels and tanks. The process blockdiagram shows limited information including design temperature andpressures, equipment, line number, Mass and volumetric flow rates andthe medium in the chemical equipment. Below is information to beincluded (Sinnott, 2005):

Stream composition m/mtotal, and flow rate of each individual componentin kg/hr.

Total stream flow rate, kg/hr

Stream temperature, degrees Celsius preferred

Nominal operating pressure

Stream enthalpy, kJ/hr.

FIG. 8-2 is a process block diagram Following the chemical engineeringstandards were every block represent a stage in a process system:

8.4. Process Flow Diagram

FIG. 8-3 process flow diagram specifies the major process units neededfor a 10 metric tonnes per hour feed stock mass flow rate operatingtemperatures and pressures as well as equipment sizing and designcapacities.

The following are the mass and energy balance as well as diagram key.

Stream Name S1 S2 S3 S4 S5 S6 S7 Mass Flow Rate 0 10 10 9.2 0.644 2.760.644 (tonne/hr) Temperature (C.) 5 25 250 550 200 200 90 Pressure (Atm)3 3 3 2 2 2 Feed stock Mass Composition LDPE 0.2 0.2 0.2 HDPE 0.2 0.20.2 PS 0.1 0.1 0.1 PP 0.1 0.1 0.1 PETE 0.4 0.4 0.4 Products PetroleumGas 0.08 (Methane) Gasoline 0.92 (Cyclohexane) Diesel (decane) 1.0Tax/Wax — —

8.5. Mass and Energy Balance Calculations 8.5.1. Basis of Calculation

In our Basis of Calculation and based on the statistical values ofcommon thermoplastic waste materials in Ontario, here are the FollowingMass Compositions of Streams which is expected to be our feed stream forMPW (municipal plastic waste) in Ontario:

Stream Number: S1

Mass Fraction: LDPE: 0.2 HDPE: 0.2 PETE: 0.4 PS: 0.1 PP: 0.1

Mass Flow rate=10,000 kg/hr (87,660 Tonne per Annum, 87.6 KTA), T=25 CP=1 atm

Mass Flow rate (10 tonne/hr)

Molecular Mass Mw (T) ofMixture=(mLDPE*MLDPE)+(mHDPE*MHDPE)+(mPETE*MPETE)+(mPP*MPP))+(mPS*MPS)(S. Mostafa Ghasian, 2008)

Referring to, the molecular masses Mw are: (Biron, 2007)

MLDPE=28.06376 g/mol

MHDPE=28.05376 g/mol

MPETE=192.1711 g/mol

MPP=42.08 g/mol

MPS=104.1 g/mol

The Granulator aims to reduce the PSD of Thermoplastic waste to 6-8 mm.Thus we are required to find the heat duty of granulators using Aspenone software and compare it with our manual results.

8.5.1.1. Electrical Duty of Mechanical Granulation Stage

For a 10,000 kg/hr which is equivalent to 22,046 lb/hr Typically, thehorsepower (HP) for common plastic grinders is 250 HP for 13,500 lb/hr.

Therefore, at a rate of 10,000 kg/hr the expected Horse power (HP) ofthe equipment needed is 409 HP. Therefore, required power at a rate of10,000 kg/hr is 305 KW.

8.5.1.2. Heat Duty Calculations for Raising Temperature of S2 from 30 CDegrees to 250 C

Referring to the Process Plow diagram and simulation, and to (WunderlichM. V., 1990) we can find the Cp, specific heat capacity of Polymers thusdetermining the Heat Duty required for raising the temperature of ourmixture from 30 C degrees to 250 C.

Specific Heat Capacity of LLDPE, HDPE and PETE In (Biron, 2007), p. 238the thermal properties of LDPE, HDPE is illustrated

Specific Heat Capacity (cal/g.C) LDPE=0.55 cal/g.C, HDPE=0.55 cal/g.C.On page 424 it I illustrated that the Specific Heat Capacity (cal/g.C)PET=0.31 cal/g.C

Specific Heat Specific Heat Thermal Capacity Capacity ConductivityPlastic Material (S.H.C) cal/g · C. (S.H.C) J/kg · C. W/(m · K) LDPE,Low 0.55 2302.74 0.30 to 0.34 Density Polyethylene (LDPE) HDPE, High0.55 2302.74 0.46 to 0.52 Density Polyethylene PETE 0.31 1297.908 0.15to 0.24 (polyethylene Tetraphalate) PP 0.406038 1700 0.17 to 0.22(polypropylene) PS 0.3105 1300 0.033 (Polystyrene)

Specific Heat Capacity of Thermoplastic Mixture

q LLPE=(2302.74) (0.2) (10,000 kg/h) (90)=414.493 MJ/h=115.14 KW

q HDPE=(2302.74) (0.35) (10,000 kg/hr) (90)=725.353 MJ/h=201.49 KW

q PET=(1297.9) (0.45) (10,000 kg/h) (90)=525.649 MJ/H=151.57 KW

Total Heat Duty (Q) for raising the temperature from 30 C to 120 C of10,000 kg·hr Granulated polymer mixture=115.14 KW+201.49 KW+151.57KW=468.2 KW with 2,000 kg/hr (21 KW)=489.2 KW

8.5.1.3. Thermal Cracking Reactions Mass and Energy Balance

Ea Activation Energy Needed for the Reaction

(Assuming First Order Reaction, and calculating using Arrhenius equationof order (Elham Khaghanikavkanil & Farid, 2010)) In the thermal crackerwe will calculate the reaction enthalpies, for thermally cracking athermoplastic mixture to oil products through Pyrolysis reactions.Polyethylene has a molecular formula of —(CH2-CH2)_(n) and severalkinetic studies have been done in order to determine heat of reaction ofpyrolysis of polyethylene to various oil products. (Gan, 2007)

Using the Kinetic Reaction Equation for Range of Pyrolysis at 450 C to550 C.

$K = {{Ko}\mspace{14mu} {\exp ( \frac{- {Ea}}{RT} )}}$

Polyethylene Enthalpy calculations Ea=376 KJ/mol, KO=3.2E24 (1/sec),(Ceamanos, Jet, al, 2000)

(Rate coefficient at 450 C) K=2.184068 sec⁻¹

The energy to be supplied per kg of thermoplastic is around 1047 KJ/kg.Therefore, Heat Duty needed (Gao, 2010):

Q pyrolysis reaction=(10,000 kg/hr) (1047 kJ/kg)/(3600 s)=2908.33 KW

FIG. 8-4 shows the energy consumption in major process units in athermoplastic-to-oil facility.

8.6. Aspen HYSYS Simulation and Justification

Using Aspen ONE® Version 8.8 for simulation of Thermoplastic wasteMixture to oil products in a pyrolysis reaction at atmospheric pressure(1 atm) and Temperature conditions ranging from 380 C to 540 C. Reactionresidence time are also to be included in our settings.

Stream S1 (Inlet Stream) with reference to FIG. 8-5

T=30 C, P=3 Bar, Stream Number: S1, Mass Flow rate: 10,000 Kg/hr (10tonnes/hour)

S1 Stream Mass Fraction Composition LDPE: 0.2 HDPE: 0.2 PETE: 0.4 PS:0.1 PP: 0.1

Adding thermoplastic components such as polyethylene LLDPE and HDPE,Polyethylene-Tetraphalate, Polystyrene and polypropylene in the ChemicalProperties is illustrated in FIGS. 8-6 and 8-7.

Stream Class is a useful feature in Aspen HYSYS in which the stream isclassified as Conventional (dissolved) Liquids or solids,non-conventional (non-dissolved) solids were PSD (particle sizediameter) for non-conventional solids need to be specified, illustratedin FIG. 8-8.

FIG. 8-9 shows input components of reactants and products.

FIG. 8-10 shows expected Petroleum Products from pyrolysis Reactions.

Propane, C3H8, represents LPG, Liquefied petroleum gas. N-DODECANE CH3(CH2) 10CH3, represents hydrocarbon diesel. While, Cyclohexane, C6H12,represents hydrocarbon gasoline.

8.6.1. Pyrolysis Reactor Operating Conditions

In Reactor specifications, as shown in FIG. 8-11, constant reactiontemperature is set at 500 C and reaction pressure set at 2 bar with nocatalyst loading.

Reactor settings shown in FIG. 8-12, including Stop Criteria, MassFraction of reactants to be 0.99, while operating times was set to be 1hour as a batch reactor.

This unit receives thermoplastic waste solids and granulates them tosmall granules between 6-8 mm hole diameter size. It is beneficial toensure that thermoplastic particles are small in size in order toincrease surface area for effective heat transfer to enable thethermoplastic mixture to change to a liquid/molten state. (Sinnott,2005) It is useful to specify mass fractions in automated or manual mode(e.g., GGS, RRSB) or enter dispersion parameters derived fromexperimental data). (Reimers, 2013)

FIG. 8-13 is an image from a plastic granulator energy simulation.

FIG. 8-14 shows specifications of the plastic solid granulator.

FIG. 8-15 shows a thermoplastic preheater from 30 to 250 C.

Using Aspen HYSYS Software Simulation, Q (heat energy) required toconvert thermoplastic mixture from solid to liquid at 10,000 kg/hr MassFraction: LDPE 0.2|HDPE 0.35|PET 0.45

Q=501.988 KW

The difference between Manual Calculations and Simulation results is7.21% using high pressure Steam as heating utility.

8.7. Economic Analysis

In this chapter and through our economic calculations, we will adaptbased on the Canadian Market prices (CA $) for utilities, capital andoperating costs. Based on economic analysis we can calculate pricing forcapital equipment, operating costs and compare prices for differentoperating routes. It is to be noted that economic evaluation is usefulduring the development stage of a process design to access itsprofitability. (Timmerhaus, 2002) It is during the preliminaryevaluation associated with Laboratory scale experiments and researchsamples of final products. As soon as the final product design iscomplete, economic evaluation shall be done. The economic analysis is tobe carried out on the Mass and Heat Balance sheet, and the finalizedconceptual design of the process system. (Timmerhaus, 2002)

8.7.1. Optimum Design and Optimum Economic Design

As mentioned earlier in this report, there are several alternativemethods which can be used for any given process or operation. Forexample, formaldehyde can be products by catalytic dehydrogenation ofmethanol, by controlled oxidation of natural gas, or by direct reactionbetween CO and H2 under special conditions of catalyst, temperature andpressure. (Timmerhaus, 2002) It is the responsibility of the chemicalengineer to choose the best process and to incorporate into his designthe equipment and methods that will give the best results. In our reportwe will aim for the optimum engineering design to achieve the optimumoperating and economic design. (Timmerhaus, 2002)

Optimum economic design is achieved if there are two or more methods forobtaining exactly equivalent final results, the preferred method wouldbe the one involving the least total cost. This is the basic definitionof an optimum economic design. (Timmerhaus, 2002)

8.7.2. Capital Investments

Before an industrial plant is put into operation, a large amount ofmoney must be supplied to purchase or install the necessary machineryand equipment. The capital needed to supply the necessary manufacturingand plant facilities is called a fixed capital investment while thatnecessary for the operation of the plant is termed the working capital.

Total Capital Investment=Fixed Capital Investment+Operating CapitalInvestment

Below are the sub-categories of fixed and operating capital investments.

Breakdown of fixed Capital Investment items for a chemical plant(Timmerhaus, 2002)

Direct Costs

a) Purchased Equipment

b) Purchased equipment Installation

c) Instrumentation and controls

d) Piping

e) Electrical equipment and materials

f) Buildings (including services)

g) Yard Improvements

h) Service Facilities

i) Land

Indirect Costs

a) Engineering and supervision

b) Construction Expenses

c) Contractor's fee

d) Contingency

8.7.2.1. Marshal and Stevens's Equipment-Cost Index

The Marshal and Stevens equipment cost index is divided into twocategories, the all industry equipment index and the process industryindex. (Timmerhaus, 2002)

The Model uses the Following equation to calculate present cost PresentCost=

$\frac{{index}\mspace{14mu} {value}\mspace{14mu} {at}{\mspace{11mu} \;}{present}\mspace{14mu} {time}}{{index}\mspace{14mu} {value}\mspace{14mu} {at}\mspace{14mu} {time}\mspace{14mu} {original}\mspace{14mu} {cost}\mspace{14mu} {was}\mspace{14mu} {obtained}} \times {original}\mspace{14mu} {{cost}( {{Timmerhaus},2002} )}$

The Marshall and Stevens equipment cost index takes into considerationthe cost of machinery and major equipment plus costs for installation,fixtures, tools office furniture and other minor equipment. Below is thelist of equipment based on our process system design where capital andoperating costs are calculated. The table is organized into direct andindirect costs statistics on a chemical plant.

Component Range % Median % Direct Costs Purchased Equipment 20-40  32%Purchased-Equipment Installation  7.3-26.0 12.5%  Instrumentation andControl (installed) 2.5-7.0 4.3% Piping (installed) 3.5-15  9.3%Electrical (installed) 2.5-9.0 5.8% Buildings (including services)6.0-20  11.5%  Yard Improvements 1.5-5.0 3.2% Service Facilities(Installed) 8.1-35  18.3%  Land 1.0-2.0 1.5% Indirect Costs Engineeringand Supervision 4.0-21  13.0 Contruction expense  4.8-22.0 14.5Contractors Fee 1.5-5.0 3.0 Contingency  6.0-18.0 12.3

It is often necessary to estimate the cost of a piece of equipment whenno cost of data is available for a particular size or operationalcapacity involved. Good results can be obtained using the logarithmicrelationship known as the six-tenths factor rule. (Timmerhaus, 2002)

According to this rule if the cost of a given unit at one capacity isknown, the cost of a similar unit with X times the capacity if the firstis approximately (X)^(0.6) times the initial cost.

${{Cost}\mspace{14mu} {of}\mspace{14mu} {equipment}},{a = {{Cost}\mspace{14mu} {of}\mspace{14mu} {equipment}\mspace{14mu} {b( \frac{{capacity}\mspace{14mu} {of}\mspace{14mu} {{equip}.\mspace{14mu} a}}{{capacity}\mspace{14mu} {of}\mspace{14mu} {{equip}.\mspace{14mu} b}} )}^{0.6}}}$

A more detailed and accurate exponent for equipment cost vs. capacitycan be seen in (Timmerhaus, 2002)

8.7.2.2. Estimation of Fixed Capital Investment Based on Plant Capacity

This method is known as seven-tenths rule for process Plants. (Don W.Green, 2008) The Formula is as follows:

${{Cost}\mspace{14mu} {of}\mspace{14mu} {Plant}\mspace{14mu} B} = {{Cost}\mspace{14mu} {of}\mspace{14mu} {Plant}\mspace{14mu} {A( \frac{{capacity}\mspace{14mu} {of}\mspace{14mu} {Plant}\mspace{14mu} B}{{capacity}\mspace{14mu} {of}\mspace{14mu} {Plant}{\mspace{11mu} \;}A} )}^{0.7}}$

This method will be our main method for equipment cost estimation inorder to develop a reliable equipment cost analysis for pyrolysis ofthermoplastic waste to oil products. It is also crucial to include theMarshal and Stevens equipment cost index to update the purchase cost ofthe equipment/asset. (Timmerhaus, 2002). Pg. 108-109

8.7.3. Thermoplastic to Oil Chemical Economic Analysis

As discussed in mass and energy balance, our mass flow rates are 87,660Tonne per Annum, 87.6 KTA of thermoplastic waste.

Therefore the expected Fixed Capital Cost based on choosing processindustry for a solid-fluid processing plant. (Timmerhaus, 2002). AlsoCEPCI Index for November 2015 is available (CEPCI, 2015) in order toupdate prices to 2016 Cost Index using Marshall and Stevens method

8.7.3.1. Purchased Equipment Estimate

The cost of purchased equipment is the basis of several predesignmethods for estimating capital investment prices and can be dividedconveniently into groups as follows:

Processing equipment

Raw-Materials handling and storage equipment

Finished Products handling and storage equipment

Referring to example in (Don W. Green, 2008) a 620.9 kg/hr of Product Xhas an initial investment of the following:

Fixed Capital Investment=$80,000

Land=$25,000

Working Capital=$120,000

-   -   Scaling up for our 10,000 Kg/hr Project we get the following        results using cost estimation equations.

$\begin{matrix}{{Cost}_{P\; 20} = {{{\$ 800000}( \frac{10000}{620.9} )}^{0.67}\frac{{CE}\mspace{14mu} {Index}\mspace{14mu} 2015}{{CE}\mspace{14mu} {Index}\mspace{14mu} 2008}}} \\{= {{{\$ 800000}( \frac{10000}{620.9} )}^{0.67}\frac{553.4}{575.4}}}\end{matrix}$

Therefore a 10 metric tonne per hour pyrolysis plant in 2015 accordingto Chemical engineering cost Index scale up Fixed Capital investment is$6,723,608.0667

8.8. Life Cycle Assessment

Life cycle assessment is a technique used to assess environmentalimpacts associated with all the stages of product's life cycle includingraw materials, materials processing, manufacturing, production andpackaging. A vital criterion for life cycle assessment is also assessingalternatives of pyrolysis oil production. (J. F. Peters, 2015) The goalof the LCA is also to estimate and compare the environmental impactsthat can be avoided by implementing pyrolysis oil production. The LCAcompares plastic to oil pyrolysis plant in comparison with a crude oilrefinery. The following assumptions are made in the block diagramcomparison:

-   -   For both scenarios, transportation of waste is ignored by        assuming that both the plants were in same distance and        transportation has a relatively small contribution of        environmental burden in the overall waste life cycle. (Zaman,        2013)    -   Municipal solid waste has the block diagram shown in FIG. 8-16        and syngas is used in electricity production. (C. Young, 2010)

Below are the LCA details for the chosen two recycling chemical plants:

Plastic Waste Plastic to Oil Pyrolysis Gasification Plant Plant NetEnergy Production to 685 571 Grid (KWh/ton) Capital Investment ($ per160,675.6 173,873.8 ton) Operating and 13,743.6 14,387.4 maintenanceCost ($ per ton per year) Expected revenue per 800 6000 ton of feedstock ($ per ton)

Carbon dioxide emissions are also much lower in pyrolysis in comparablewith combustion or other waste treatment methods. (J. T. Conesa, 2008).CO2 emissions of plastics such as PVC or polyester for pyrolysiscompared to combustion.

As seen below, pyrolysis reactions emit much lower carbon dioxideemissions in comparable with combustion.

Combustions at 850 C. Pyrolysis at 850 C. Material (CO2 emissions pg/g)(CO2 emissions pg/g) Polyester 14 negligible PVC 4500 215

8.9. Conclusion

Large scale Plastic to Oil production plants include major process unitsstarting with granulation, preheating, pyrolysis reaction, Light andheavy oil separation units, wax removal units. Aspen HYSYS simulationshows highest energy consumption in the pyrolysis reactor 125.8 MW for87.6 KTA Plastic to Oil pyrolysis plant. Implementation of thermalplasma in pyrolysis reactions can significantly reduce the energyconsumption. Pyrolysis oils include light and heavy components whichneed to be separated using flash separators. Tar is reduced by ensuringnitrogen conditions. The Carbon dioxide emissions are much lower forpyrolysis in comparison with combustion methods.

In terms of capital investment, pyrolysis has nearly 8% more capitalinvestment that gasification chemical plants. However, pyrolysisproduces liquid products in comparison with only syngas production forgasification chemical plants. Pyrolysis oil has higher selling valuethan syngas and can be used for transport or combustion engines unlikesyngas is mainly used for electricity production.

9. Conclusion and Future Work 9.1. Conclusion

A direct current thermal plasma circuit was used in thermoplastic to oilproducts pyrolysis reaction with chosen residence time of 30 minutes andoperating temperature of 550 C. A 7 mL was collected from a 15-gramthermoplastic sample and results showed existence of n-butyl benzene,undecane and other hydrocarbon mixtures, the yield conversion achievedin a 1 L pyrolysis reactor under −0.95 bar was nearly 60 wt % tohydrocarbon pyrolysis oil, the hydrocarbon gases were tested forflammability and wax and tar was collected. It was also shown thatexistence of oxygen increases tar production.

The direct current thermal plasma showed better temperature profileusing a K-type thermocouple in comparison with a 220 V, 4.8 A, 1056 Wona 15 gram LDPE sample, the residence time for both reactions were chosento be 30 minutes, thermal plasma showed faster gaseous products andlower content of unreacted thermoplastics and achieve same productyields of pyrolysis oil showing benzene and butyl benzene as majorproducts with minor quantities of undecane. Hydrocarbon gases weretested for ignition and showed high flammability and can be used forcombustion purposes.

The direct current thermal plasma is a reliable source of thermal energyand can be scaled up for usage in large scale pyrolysis reactors underoperating conditions −0.95 bar and 550 C. The direct current thermalplasma used was 30 mA and 9000 V thus consuming 270 W. Pure nitrogen99.99% should be used to prevent oxidation or unwanted reactions tooccur during pyrolysis. Gaseous products are only allowed to condenseafter the mentioned residence time of 30 minutes which allow hydrocarbonliquids and waxes to condense which is later collected and weighted tocalculate product yield.

To conclude, the direct current thermal plasma system operates at vacuumpressure at 60 Hz and achieves better temperature profile in comparisonwith other heating methods, thermoplastic sample shows thermal crackingat a faster rate than other heating methods, gaseous products areallowed to condense and hydrocarbon pyrolysis oil weight 59 wt % whiletar is reduced by providing an oxygen-free environment.

9.2. Future Work

The same experimental setup can be used on a variety of thermoplastics,where the chemical compositions of oil products are identified, followedby categorizing thermoplastics that produce heavy oils and others thatproduce light oil products. If diesel is the desired final product,specific thermoplastics can be selected to achieve diesel liquidproducts. Added to that, the ignition properties of the pyrolysis oilare to be studied for LDPE, HDPE, PS, PP and PETE since they form morethan 90 wt % of pyrolysis oil.

In order to improve reaction kinetics, HZSM-5 and HUSY catalysts maypossibly be used to reduce residence time and operating temperatures aswell as their performance with thermal plasma torches. RF thermal plasmaat 13.56 MHz frequency may be used with individual thermoplastics andthermoplastic mixtures to confirm its benefit.

9.3. Contribution

This work illustrates the integration of direct current controllablethermal plasma circuit to be used in thermoplastic to oil conversionreactions. While pyrolysis reactions consume large amount of thermalenergy (e.g. around 1047 KJ/Kg in a 30 minute reaction residence time),the thermal plasma can achieve such heat energy at a much lower powerconsumption to traditional electric heaters at a much higher efficiency.Also, thermal plasma temperature can be easily controlled which isbeneficial in achieving desired products in thermoplastic to oilconversion reactions. Thermal plasma also works excellent in inertconditions in nitrogen gas and can be used in large scale pyrolysischemical plants. In the experimental setup, a 270 W Direct currentthermal plasma were used against a 1056 W electric heater on a 15 g LDPEsample and pyrolysis oil were collected with a product yield of 59 wt %.The pyrolysis oil sample shows butyl-benzene as a major product andexistence of small traces of decane-diesel range fuel. The directcurrent thermal plasma system can be scale up and can drivethermoplastic to oil chemical recycling and achieve the required highthermal energy consumption in large scale pyrolysis reactors. The directcurrent thermal plasma jets are much more efficient to be used inpyrolysis reactors and have shown much higher temperature profiles andhave lower electrical consumption than traditional electric heaters orother traditional industrial heating systems such as industrial furnacesand thermal cracking units.

Persons skilled in the art will appreciate that there are yet morealternative implementations and modifications possible, and that theabove examples are only illustrations of one or more implementations.The scope, therefore, is only to be limited by the claims appendedhereto.

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What is claimed is:
 1. A process for converting thermoplastic waste intohydrocarbon gaseous and liquid products, the process comprising: placingin a reactor an amount of thermoplastic to be converted; depressurizingthe reactor to remove air; filling the reactor with an inert gas;subjecting the amount of thermoplastic to a thermal plasma arc sourceoperating at a select temperature profile for a preselected residencetime to produce a gaseous product; directing the gaseous product throughat least one condenser; and collecting a liquid fraction condensed fromthe gaseous product in the at least one condenser.
 2. The processaccording to claim 1, wherein the inert gas is a pressurized nitrogengas.
 3. The process according to claim 2, wherein the pressurizednitrogen gas is added to the reactor to a pressure of 1 bar.
 4. Theprocess according to claim 1, wherein the thermal plasma arc source is adirect current thermal plasma arc source.
 5. The process according toclaim 1, wherein the preselected residence time is from about 20 toabout 40 minutes.
 6. The process according to claim 1, wherein thepreselected residence time is from about 25 to about 35 minutes.
 7. Theprocess according to claim 1, wherein the preselected residence time isabout 30 minutes.
 8. The process according to claim 1, wherein thethermoplastic is selected from the group consisting of low densitypolyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS),polypropylene (PP) and polyethylene tetraphalate (PETE).
 9. The processaccording to claim 1, wherein the reactor is a closed system reactor.10. A process for converting thermoplastic waste into hydrocarbongaseous and liquid products, the process comprising: receiving afeedstock of thermoplastic to be converted; granulating the feedstock toreduce the thermoplastic to a preselected granule size; delivering thegranulated feedstock to a preheat unit and preheating the granulatedfeedstock based on a preselected preheat temperature profile; deliveringthe preheated granulated feedstock into a reactor and subjecting thefeedstock to pyrolysis based on a preselected pyrolysis temperatureprofile for a preselected residence time to produce a gaseous product;directing the gaseous product through at least one condenser; andcollecting a liquid fraction condensed from the gaseous product in theat least one condenser.